Issei Hyoudou

"I’m going to become a Harem-King!"

- Issei Hyoudou shouting out his dreams

Issei Hyoudou is the main male protagonist of High School DxD. He is a second-year student at Kuoh Academy and a member of the school's "Perverted Trio", a trio of the most perverted men in the entire student body.

He's a member of the Occult Research Club, and his rank in Rias' peerage is Pawn. His power as a Devil ranks at the bottom in the beginning (which increases as the series progresses, until eventually he becomes the strongest among the young Devils and develops his strength into SS-Class); however, on his left arm, he wields the Sacred Gear, Boosted Gear, making him a dangerous opponent to underestimate. His goal is to one day rise in rank to that of a High-Class Devil so that he can gather his own servants and create his own harem, becoming a "Harem King".

Appearance
Issei is a 17-year old high school student of average height with short spiky brown hair, with two short locks of hair behind his head, and light brown eyes. Following his training with Tannin in Volume 5, he gained a more muscular and toned build.

While he has worn various outfits throughout the series, his most commonly worn outfit is the Kuoh Academy boys' school uniform, which consists of a blazer (more commonly black, although in other media is shown with a tinge of purple or grey, with white accents) over a white, long-sleeved dress shirt with black highlights with a black ribbon on the collar, matching black pants, and brown dress shoes. However, Issei's uniform differs in the fact that he wears a red T-shirt underneath his open dress shirt and blazer, and wears blue and white sneakers in place of dress shoes.

From the end of Volume 2 to the beginning of Volume 12, Issei's left arm was transformed into that of a Dragon. In order for it to appear human, a ritual would be performed where Rias or Akeno would suck the power of the Dragon out of it, allowing it to appear human for a few days. After gaining a new body in Volume 12 through the combined efforts of Great Red and Ophis, he is now able to freely transform any part of his body into that of a Dragon.

Personality
Issei has many personality traits. Issei is first shown to be ignorant, self-centered, arrogant, and his ongoing perverted nature, often to make lecherous fantasies, and utterly obsessed with women's breasts and having his own harem. This has caused him to be instantly labeled as a pervert among the girls of Kuoh Academy and has gained him notoriety for being one of the members of Kuoh Academy's Perverted Trio.

Despite his pervertedness, Issei is kind, courageous, and unwaveringly determined of wanting to protect those who are important to him despite almost dying by the hands of his opponents. He's also very caring, "putting his nose on other peoples business" as he helped Yuuto, Koneko, and Akeno overcome their fear and hatred of their mournful past. Due to this, he gained strong friendship from his comrades and affection from most girls of the Occult Research Club. He is, however, oblivious to the feelings of the girls around him (save for Rias after his confession), often believing they are simply teasing him. Even with Rias' family telling him to use the same titles for them as Rias (Father, Mother, Brother, etc.) and other mentions of engagement activities, he still remains the same. This is due to his trauma with Raynare.

After his murder by Raynare, Issei had developed a fear of admitting his feelings to the girls, as he thought it would cause them to turn their backs on him. He acknowledged that this would never happen, but it was still an intense fear. However, by Volume 10, that fear had been overcome. Even with knowledge that the girls do have romantic affection for him, he still has problems acknowledging some of their ongoing rivalries, an example being who is the one to sit on his lap.

In battle, Issei is sometimes very stubborn, and due to his emotions, he often charges ahead towards his enemies without a second thought whenever his comrades are insulted, treated badly, or easily defeated. Azazel has stated that it is one of Issei's bad habits. Lately, he has started to become more tactical in his battles, using technique-type strategies to defeat opponents, as shown when he used the abilities of the Wyverns in a unique way to defeat Euclid. Another sign of his kind nature is that despite wanting to lose his virginity, Issei refuses to take advantage of women when they are upset, even if they themselves are willing to. This happened when Akeno appeared in front of him naked and wanted to have sex to forget about her sad past and her father. However, Issei refused, knowing it will just hurt her more, and put her clothes back on and hugged her to comfort her.

History
Initially, Issei's parents had a great deal of trouble conceiving a child, failing twice. So when Issei's mother got pregnant for a third time his father had paced back and forth in front of shinto shrine honestly wishing that this time they would succeed. When the child was finally born he was named Issei, meaning Honestly, for his father's honest prayers.

He is a childhood friend of Irina Shidou and they would always play together before she moved to England, although he thought she was a boy at the time. At some point when Issei came over to Irina's house, she kissed him while he was sleeping. Sometime during his childhood, Issei met an old man who told him and other children stories about breasts, which eventually led to Issei's fascination with them and his perverted tendencies.

He attended the same middle school with Matsuda and Motohama and the three of them started attending Kuoh Academy one year before the story, and have come to be known as the Perverted Trio to just about the entire school.

The Red Dragon Emperor's Awakening
Issei was introduced in Volume 1 of the light novels, where he is asked by Yuuma Amano to go on a date with her. However, at the end of the date, Yuuma suddenly kills him, after revealing herself as a Fallen Angel in the process. In his dying moments, Rias Gremory arrives and saves his life, after he inadvertently summoned her whilst thinking about her. The next day, after noticing some strange changes within his body, he is attacked by the Fallen Angel Dohnaseek, who critically wounds him until Rias arrives and saves him once more. He is then introduced to the other members of the Occult Research Club: Yuuto Kiba, Koneko Toujou, and Akeno Himejima, and soon learns that all of them, including Rias, are Devils. He soon learns to his surprise that he is a Devil as well. However, after learning from Rias that he can one day have his own servants, Issei then declares his dream to have his own harem, becoming a "Harem King". Later on, he meets Asia Argento, a nun, and quickly befriends her. He soon learns that she, too, possesses a Sacred Gear after using it to heal a young boy. He then guides her back to the Church, where, upon reaching near it, he gets strange chills coming from his body, forcing him to stop while Asia goes on ahead (Rias explains to him that Devils cannot go near churches as there is a risk of getting killed by the Angels' light spears).

During his first-ever battle with the Stray Devil Viser, he learns from Rias about Kiba, Koneko, and Akeno's respective traits as Knights, Rooks, and Queens, and later learns, to his disappointment, that he is a Pawn. The next night, Issei goes on another run to meet up with a client, only for the client to be killed by Freed Sellzen, a stray exorcist, upon arriving at the client's home. He is nearly overwhelmed by the berserk priest until Asia intervenes, pleading Freed to let Issei go but gets hit by him, angering Issei who fights Freed one more time but is stopped when the rest of the Occult Club intervene to bring Issei back. Fortunately, Issei eventually meets Asia again at a nearby park the next day, and the two spend the entire day together which ends with the sudden appearance of Raynare who takes Asia back after overwhelming Issei despite the latter using his Sacred Gear.

Determined to save Asia from the Fallen Angel, Issei, with Kiba and Koneko's help, manages to reach the church where Raynare is hiding while fighting Freed once more. However, it was too late and Raynare takes Asia's Twilight Healing. Escaping with Asia, Issei shares one last conversation with Asia who thanked Issei for being her friend as she dies in his hand. Determined to avenge Asia's death, Issei fights Raynare in a one-on-one duel, while initially having difficulties he successfully defeats her after activating his Sacred Gear, the Longinus, Boosted Gear's true ability. He then allows Rias to kill Raynare after the latter desperately begged Issei to save her, even going as far as saying she loves him, having seen through her ruse. After the battle, he was delighted after Rias revives Asia as one of her Bishops, sharing an emotional reunion with Asia. The next day, Issei was surprised to see Asia dressed in a Kuoh Academy uniform as Rias informs Issei that Asia has been transferred into the school and will be in Issei's class.

At the beginning of Volume 2 while having a dream about marrying Rias, Issei encountered a Red Dragon in that dream waking up shortly after. Following his daily training with Rias, Issei was shocked to learn from her that Asia will be moving in to stay with him as Rias successfully convinces Issei's parents to let Asia stay. A few days later, while getting used to Asia being at his house while having his usual school life and Devil's job, Issei gets a sudden visit from Rias, who asks to take her virginity much to his shock and surprise. Unfortunately, Rias' attempt is foiled with the appearance of Grayfia Lucifuge, a maid from the Gremory, who scolds Rias for attempting to break off the engagement set by her brother and father. Later on, Issei meets Riser Phenex, a man from the Phenex Clan who, to his shock, is revealed to be Rias' betrothed. Refusing to accept it, he activates his Boosted Gear in an attempt to face Riser one-on-one but is easily defeated by one of his Pawns.

After Rias agrees to face Riser in a Rating Game with her engagement on the line, Issei and the rest of the Occult Research Club members go to a mountain to train. He later assisted Rias in her first-ever Rating Game against Riser, in which he incapacitated three, defeated one and assisted in defeating five of Riser's Peerage before going off to face Riser. Issei, however, was incapable of doing anything as his body reached its limit due to the burden of the boosted power that is continuously placed on his body, and was nearly beaten to death by Riser, forcing Rias to resign. Later waking up in his room and being informed of Rias' defeat by Grayfia, Issei becomes frustrated and blames himself for his weakness only to be given a paper with a magic circle engraved on it by Grayfia. Arriving in the engagement party hall, Rias' brother and Satan, Sirzechs Lucifer, reveals that he set up this event as an entertainment for Rias' engagement party, which allows Issei to battle Riser one more time in a one-on-one fight with Rias' engagement on the line, and won through the strategy he formulated beforehand. Taking Rias away from the ceremony, Rias thanks Issei for what he did, kissing Issei for the first time.

Birth of the Breast Dragon Emperor
In Volume 3, Issei wakes up to a chaotic morning due to Rias who now stays with him. During the club meeting held in Issei's house due to the cleaning of the old school building, Issei's mother shows Issei's childhood photos to his friends; among them include a photo of Issei and his childhood friend, Irina Shidou, which has a Holy Sword in it, with Kiba seeing the photo and remembering his revenge. He was then introduced to the Student Council members led by Sona Sitri, whom it was revealed is a High-Class, Pure-blooded Devil and the heiress of the Sitri Clan. While preparing for the ball tournament of Kuoh Academy, Issei starts to notice the change in Kiba, pressuring Kiba into revealing what is going on as Kiba reveals his goal in life, revenge on the Excalibur, as Issei learns of the ongoing situation between Kiba and the Excalibur sword. He later re-encounters his childhood friend, Irina, who is now under the Church's orders to retrieve the stolen Excalibur swords. Having found out about Yuuto's past, Issei decides to help the latter to overcome his past. To that end, Issei, Koneko, and Genshirou Saji went to find Irina and her partner Xenovia and made a temporary alliance with the Church Duo, where they will help the two of them to retrieve the Excaliburs in return for allowing Yuuto to destroy them. They eventually encounter both Freed Sellzen and Valper Galilei, engaging in a battle with the two of them who manages to escape. Their alliance was then found out by their masters and the three of them are punished for taking this action without their consent. The Occult Research Club was then confronted by Fallen Angel leader, Kokabiel who challenged the Gremory Team to a fight within the grounds of Kuoh Academy. With backup from the Sitri Team who formed a barrier surrounding the school, the Gremory Team engaged Kokabiel, Freed, and Valper. While the Gremory Team and Xenovia were able to defeat the Cerberus sent by Kokabiel and Freed who was wielding the Fused Excalibur, they eventually engaged Kokabiel in a battle and were overwhelmed by the latter who revealed the death of the Biblical God. The Gremory Team, however, were saved by the sudden interference of Vali Lucifer, who came to retrieve Kokabiel and Freed under Azazel's orders.

In Volume 4 of the light novels, Rias introduced her other Bishop, Gasper Vladi, to Issei, Asia, and Xenovia. Issei later helps in Gasper's training on how to use his Sacred Gear. Prior to the meeting of the Three Factions, while visiting Akeno at the shrine she used to stay at, he receives St. George's Dragon Slayer sword, Ascalon, from the Archangel Michael, and learned of Akeno's identity. He later assisted in fending off the Khaos Brigade members who came to kill the leaders of the Three Factions during the peace negotiations, as he and Rias go to rescue Gasper who was being used by the Khaos Brigade. After successfully rescuing Gasper from the Khaos Brigade, Issei, Rias, and Gasper are surprised at the sudden betrayal of Vali Lucifer who then goes on to fight Issei. Using the bracelet given to him by Azazel, which act as a substitute for the sacrifice needed to use the Scale Mail, he begins his duel with Vali. While initially incapable of doing much against Vali, Issei uses Ascalon to break Vali's shield and manages to transfer Ddraig's power to Vali's Scale Mail, forcing it to temporarily stop its function and land an attack on Vali. Issei, however, was shocked at the recovery rate of Vali's Scale Mail and with few options left, Issei decides to take a risk by implanting Albion's power to the Boosted Gear, which was successful and created the Dividing Gear. Vali, who was interested at the situation, goes on to say that he will halve all of Issei's surroundings, which Azazel adds on that breasts will be halved as well, angering Issei to the point that he is able to overwhelm Vali in his usual Balance Breaker form. The battle, however, was ended abruptly by the sudden intrusion of Bikou who came to retrieve Vali before he could activate his Juggernaut Drive.

In Volume 5, he goes to the Underworld with Rias and his friends for the Young Devils Gathering. Upon arriving at the Gremory region, Issei, along with Rias and her peerage, is greeted by the servants of the Gremory household before meeting Rias' mother, Venelana Gremory, and nephew, Millicas Gremory. During that time, he was taught how to read and write the Devils' alphabet, proper table manners, dance classes and how to interact with people with high social status. Before the ceremony for the Young Devils Gathering, Issei meets the four other Devils that are chosen for the competition: Sairaorg Bael, Seekvaira Agares, Zephyrdor Glasya-Labolas, and Diodora Astaroth. After the Rating Game between Rias and Sona was determined, he was forced to train with the former Dragon King, Tannin, in one of the mountains in the Gremory region, and obtained a great stamina that he can use when he gained his Balance Breaker. Issei, however, did not attain his Balance Breaker until the fight against Kuroka and Bikou where he gained full-access to his Balance Breaker after poking Rias' breasts. He then assisted Rias in her Rating Game against Sona. While he manages to defeat Saji, he lost due to blood loss which was set up as a plan by the Sitri Group to defeat Issei. Before disappearing however, Issei reveals his new move, Bilingual, which allows him to talk with female breasts and learned of the Sitri Group's strategy, allowing Rias' team to win the match in the end. While the Occult Research Club is leaving the Underworld to head back to the human world, the group was surprised by the sudden appearance of Diodora Astaroth, a Devil whom Asia healed in the past, who came to propose to Asia.

In Volume 6, Issei and his friends accompany Rias to the television station of the Underworld for an interview for the Young Devils Tournament where they met Sairaorg and his Queen, Kuisha Abaddon, who just finished their interview and told the Gremory Team that he wants to face them with pure power only. During Rias and Diodora's scheduled Rating Game, the match was interfered by the sudden appearance of the Khaos Brigade and the revelation of Diodora's alliance with them before kidnapping Asia. The Gremory Team would then go on to defeat Diodora and his peerage and rescue Asia until the sudden appearance of Shalba Beelzebub who sends Asia to the Dimensional Gap. This act caused Issei to activate the Juggernaut Drive of the Boosted Gear, due to the negative feelings that appear after the apparent "death" of Asia, and made him go berserk. He defeated Shalba, even biting off his left hand, but was incapable of stopping himself, until Azazel and Sirzechs composed an Oppai Dragon song and used Rias' breasts as a switch to help him release the Juggernaut. Issei then witnessed the appearance of the Great Red, who was swimming in the Dimensional Gap, later felling unconscious. He wakes up in his room, having a discussion with Sirzechs through hologram regarding Juggernaut Drive. He then runs with Asia on their three-legged race and receives cheers from Occult Research Club members and Azazel. After winning first place, Asia tends to Issei behind the gym, where she kisses him and confesses that she loves him.

The Heroic Oppai Dragon
In Volume 7, Issei goes on a date with Akeno, which ends with both of them meeting Odin, Rossweisse, and Baraqiel, Akeno's father and Fallen Angel leader, who served as Odin's bodyguard at that time. The Occult Research Club is then attacked by Loki who came to kill Odin and create Ragnarok. Issei faces off against Loki in a fight but was dominated by the arrival of Fenrir. Issei and his friends are, however, saved by the timely arrival of Vali Lucifer and his team. The two teams eventually decided to work together to fend off Loki and Fenrir, asking the advice of the Dragon King, Midgardsormr, on how to defeat Loki and Fenrir. During the final battle against Loki, Issei wielded a replica version of Mjolnir, a hammer used by Norse God Thor. While initially incapable of fully using the Mjolnir, Issei gains the ability to use it after helping Akeno reveals her true feelings and make amends with her father through the help of the Breast Fairy send by he Chichigami, adding with the Holy Lightning of Baraqiel and Akeno and allowing them to defeat Loki. The group later returned to their clubroom where Akeno kisses Issei and confesses that she loves him in front of everyone, which only angers the other girls.

In the Extra Life of Volume 8, Issei and Rias went the Underworld and underwent a ceremony at the Ruins of Connection to test his suitability as Rias' future husband. Throughout the ceremony, Issei and Rias faced four trials set up by the Satan Rangers. In the first trial, Issei and Rias had to dance; in the second trial, they were tested on table manners; and in the third trial, on the history of the Gremory Clan and general knowledge in the Underworld, all of which they successfully passed before moving to the final trial. In the final trial, Issei was forced to fight Sirzechs/Satan Red and was completely overwhelmed by the latter, until Grayfia's advice on using Rias' breasts as a power-up allowed Issei to use one final Dragon Shot, but still lost after Sirzechs negated the attack and retreated after Issei loses consciousness. After the ceremony, Ajuka Beelzebub, one of the Four Satans and the original creator of the Evil Pieces system, remodeled Issei's Piece to adapt to the powers of Ddraig.

In Volume 9, Issei and the rest of the second-year students go to Kyoto for their school trip. In the train, Issei enters the depths of the Boosted Gear, where he meets one of the past possessors of the Boosted Gear who provides him with a box that unlocks his potential and its possibilities. During the trip, Issei was attacked by several Youkai led by Kunou, who thought that he is the one responsible for capturing her mother, Yasaka, the leader of the Youkai. While they manage to clear off the misunderstanding, Issei and his friends are soon confronted by the culprits who captured Yasaka: the Hero Faction led by Cao Cao. While the first fight was cut short by the interference of Le Fay Pendragon and Gogmagog from the Vali Team, Issei and his friends are forced to face off with the Hero Faction one more time to rescue Yasaka from them.

During the fight, after seeing one after another of his friends being defeated, Issei curses his own powerlessness again, but this time with Belzard and Elsha's advice, Issei successfully achieved the Illegal Move Triaina due to his desire to protect his friends and Rias' breasts, allowing him to change the Scale Mail armor through Promotion. With the new found power, Issei manages to temporarily overwhelm the entire Hero Faction before succumbing to the exhaustion. The team, however, was rescued by the sudden appearance of Sun Wukong who fends off the Hero Faction and using his Senjutsu to rejuvenate Issei, allows him to use one more attack, which he landed on Cao Cao's eye. After coming back from Kyoto, the team was scolded by Rias for not calling her to help them, before Azazel tells the group that Ravel is transferring to the Kuoh Academy, much to the dismay of the girls of the Occult Research Club.

In Volume 10, after finishing another Oppai Dragon campaign, Issei and Rias met Rias' mother, Venelana, who complimented them for their hard work, before scolding Rias for her lack of progress with Issei. Rias would then attempt to seduce Issei by trying to have sex with him in the sauna room of the Hyoudou Residence. Issei, however, fails to understand and calls Rias "President", greatly saddening and angering the girl, asking him what is she to him. He later reveals to Koneko, Asia, and Akeno (who are trying to "heal" him) that his experience with Raynare made him fear women, after he planned his whole first date with her, only to be killed and treated terribly, made him afraid to call girls by their first name, and also afraid of being disliked by other girls or rejected if he showed his feelings again. The girls, however, quickly object to this, and Raynare's "curse" is lifted from Issei's heart.

During Rias' Rating Game against Sairaorg Bael, Issei fought against Sairaorg's Bishop, Coriana Andrealphus, and Queen, Kuisha Abaddon, both of whom he defeats, before facing off against Sairaorg and his Pawn, Regulus, in the final match with Rias. During the match, Issei was doing well against Sairaorg until Sairaorg fused with Regulus to use his Balance Breaker, overwhelming Issei. Issei, however, was able to overturn the situation by gaining access to the True Queen, achieving Cardinal Crimson Promotion which combines the power of the Rook, Knight and Bishop to his Balance Breaker armor while changing it to crimson. Using his newly acquired powers, Issei manages to fight on par with Sairaorg, successfully defeating the man in a fist fight after Sairaorg lost consciousness, Issei hugged him, saying his thanks, before passing out. Following his victory, Issei cannot hold back his feelings for Rias and confesses to her, calling her by her first name for the first time. She accepts his feelings in tears of joy and the two officially become a couple, although it seems none of the other girls (Akeno, Xenovia, Asia, Koneko, Irina, and Ravel) have given up on Issei.

In Volume 11, Issei, like the rest of the Gremory Team, are surprised to see Ophis, accompanied by Le Fay and Kuroka, come to their house, which was set up by Azazel after Ophis claims that she wants to observe Issei. Later, Issei, Akeno and Yuuto go to the Glasya-Labolas territory to take the promotion test to become Middle-Class Devils. While the group is resting after the test, they are ambushed by Cao Cao and Georg who came to steal Ophis' powers. The battle ended with the Gremory and Vali Teams losing to Cao Cao and Ophis' powers stolen. Both teams were then attacked by a legion of Grim Reapers and Siegfried. They eventually overcame the situation by having Issei use Rias' breasts to replenish Issei's magic and successfully force their enemy to retreat, until Shalba appeared with a kidnapped Leonardo, forcefully activating Leonardo's Balance Breaker, which creates 13 gigantic monsters to destroy the Underworld, and kidnapped Ophis.

Near the end of the volume, Issei went to rescue the kidnapped Ophis from Shalba who escaped into a crumbling dimension field. Issei eventually caught up to Shalba and the two of them fought one last time before Issei kills him. During the fight, however, Shalba manages to inject an arrow infused with Samael's blood, which led to Issei's death.

In Volume 12, Issei's original body is destroyed due to Samael's curse, but he then gains another body with the help of the Great Red and Ophis. He returns and successfully saves the child who was taken hostage by Jeanne and Heracles, defeating the former easily. He has his third encounter with Cao Cao, but was easily outmatched by the latter, even with Rias using her ability to recharge Issei's power, until Issei used a bullet from Gogmagog that has Samael's blood on it, on Medusa's eye, that Cao Cao was using, reversing the situation. In order to turn back the tide of battle, Cao Cao attempts to activate the Truth Idea, but unsuccessfully, as its effects depend on God's will in the Holy Spear, and it will be different depending on what the will chooses. The True Longinus has chosen the wish in Issei's heart, rather than Cao Cao's ambition, thus Cao Cao is defeated. At the end of Volume 12, Issei is officially promoted into a Middle-Class Devil, along with Akeno and Yuuto. Afterwards, Rias and Issei plan on going out on a date as promised earlier, with the rest of the Occult Research Club members (including the guys, much to Issei's distress) deciding to come with.

In the Extra Life of Volume 13, Millicas goes to the Hyoudou Residence and temporarily stays with them. He later has a mock battle against Issei, Kiba, and Gasper. Despite losing to them, Issei notes that his power is extraordinary and his talent is said to be the same as that of Vali. Later, when Sirzechs asked him whether he liked Satan Red or Oppai Dragon, Millicas chose the latter. This made Sirzechs sad, and it became worse when he saw Issei and Millicas getting along. At the end, Issei calls him Millicas instead of Millicas-sama. Issei is later given a familiar, the living Norse flying ship Skíðblaðnir, by Surtr Second (which he later names Ryuuteimaru).

The Legend of Oppai Dragon and his Lively Companions
In Volume 14, Issei meets the Director of the Magician Council, Mephisto Pheles, regarding the pact between the Occult Research Club and Magicians. He later attended the negotiation with the Vampires who were led by Elmenhilde Karnstein who wanted Gasper to join her clan, the Carmilla Faction. He was completely ignored when he asked her a question due to his status as a servant. Several days later, while attending his class, Issei was attacked by three Stray Magicians who distracted him so that they could kidnap the first-year students of the Occult Research Club. He, along with the other members of the Occult Research Club and the Student Council then go to battle them and easily defeated the Stray Magicians and the Magicians from Khaos Brigade before a voice called Issei, Akeno, Xenovia, Asia, Irina, Rossweisse, Saji, and Sona to meet him. The group was sent into a "factory" built in the Dimensional Gap that was used to create artificial Phoenix Tears using clones of the Phenex Clan. After some talk with the supposed leader, he summons Grendel and Issei was forced to battle him one-on-one, but was overpowered throughout the fight until he used Ascalon's Dragon Slayer abilities to turn things around. It was then that the leader of the Magicians, Euclid Lucifuge, Grayfia's younger brother, calls Grendel to retreat while revealing himself to Issei and the others.

In Volume 15, while Issei and Ravel are selecting magicians to make a pact with, Akeno, Sona, and Bennia entered his room to discuss what the Sitri and Gremory groups would do while Rias and Yuuto are in Romania. They did their discussion in the underground pool when Kuroka and Le Fay arrived and was shocked when Kuroka mentioned that they fought the Evil Dragon, Aži Dahāka. Griselda Quarta, Dulio Gesualdo, and Tobio Ikuse later arrived and asked Issei if it is okay for them to help train the group to which Issei happily agreed.

In Volume 16, Issei, along with the Occult Research Club members, Bennia, and Loup Garou went to Romania to aid Rias and Yuuto who were confined in the Tepes castle, reuniting with the two when they arrived at the castle. They were then taken to the throne room to meet the new "King", Valerie Tepes and the new mayor, Marius Tepes as the group was angered by Marius' action and the latter's claim that he could do so without fearing for his life because of his bodyguard, the Evil Dragon Crom Cruach. After the meeting was over, Issei and the others met an old man wearing a Lucifer outfit who he was shocked to learn that the man was Vali's grandfather, Rizevim Livan Lucifer and vehemently refused Rizevim's proposal to join his group.

Issei then participated in the attempt to stop the extraction of the Longinus, Sephiroth Graal, from Valerie and save her. Meeting Grendel again, Issei and his friends team up to battle Grendel in order to buy time for Rias to use her new move, in which they successfully dealt a serious damage to Grendel with their combine efforts. The fight, however, ended without a clear outcome, as Crom Cruach appeared and ordered Grendel to retreat. Vali then appeared as both Issei and Vali agrees to team up to face the strongest Evil Dragon. Issei in his Cardinal Crimson Queen was able to deal minor damage to Crom Cruach by using Crimson Blaster combined with Ascalon's dragon-slaying ability. The fight was stopped by Crom Cruach since he was told to stall them just for ten minutes. Issei later fought the mass-produced Evil Dragons that were rampaging at the Carmilla's castle town and was able to defeat them easily until he encountered Euclid Lucifuge. He then fought against Euclid who uses a replica of the Boosted Gear. He was overwhelmed by Euclid in his Scale Mail but was able to turn things around when he used his newly found power which allows him to create small white Dragons that can "divide" and "reflect". The fight was stopped when Rizevim and Lilith arrived and told Euclid that its time to retreat. After returning from Romania, Issei participated in the meeting for the formation of D×D and told Ravel that he wants Le Fay to be his contracted magician.

In Volume 17, Issei was suddenly asked by Rossweisse to act as her boyfriend much to his and the other girls' surprise, the reason of which was later revealed that Rossweisse lied to her grandmother about having a boyfriend. He meets Rossweisse's grandmother, Göndul, as Rossweisse's "boyfriend". He and Rossweisse then go on a date in Tokyo which ended abruptly due to Euclid's sudden appearance. Later, Issei and his friends went to the newly built Auros Academy to help teach the children. During their stay, while Issei is having a bath, Rossweisse joins in due to no hot water on the girls bath, they talk regarding her research on Trihexa, worried that she might be taken and used by the enemy, Rossweise asks Issei to kill her if it were to happen, but he refuses saying he will protect her. The academy was soon ambushed by Qlippoth, Issei then teams up with Nimura to fend off the mass produced Evil Dragons before meeting up with Saji and Koneko, as the four are confronted by Grendel and Ladon who proceeds to seal Issei inside his barriers Issei helplessly looks on as Saji and the fathers of the children are attacked ruthlessly by Grendel, until Sairaorg arrives to assist as Ladon was ordered to retreat to Agreas while Grendel remained to fight Sairaorg and Issei who teamed up and successfully defeated Grendel, allowing Koneko to seal Grendel.

Issei regroups with his allies to fend off the remaining Evil Dragons until Euclid appears and kidnaps Rossweisse as Issei and Rias proceed to pursue Euclid. Issei and Rias then confront Euclid regarding his goals as Euclid reveals that he wants to make Rossweisse his "sister" and soon after kills the magicians allied to them by changing them into living bombs, effectively destroying the school. Angered by this act, Issei proceeds to fight Euclid, successfully overpowering him after Issei manages to unlock the Longinus Smasher. After the incident with Qlippoth, which ended with Agreas getting stolen, he and his allies were informed that they are going to the Heaven's side to help with something during the winter holidays.

In Volume 18, Issei went to Heaven, alongside the Gremory group. Upon their return home they meet Irina's father Touji Shidou who had come to visit, he brings them a magic doorknob that leads to an Interdimensional Room that allows Irina and Issei to have sex without her falling. While out shopping with Irina, Touji, Xenovia and Asia, they are confronted by Masaomi Yaegaki who is wielding Ame no Murakumo no Tsurugi infused with half of Yamata no Orochi's soul and seeking revenge on Touji. They all fought against Masaomi but he manages to impale Touji and poison him, he retreats as soon as reinforcements arrive. Touji who is now hospitalized explains that Masaomi was a former subordinate of his who was executed by the Church for being in a romantic relationship with a Devil named Cleria Belial. Later, Issei and the Occult Research Club meet up with Zekram Bael, he then revealed to them that he ordered with the permission of Heaven and the Church the death of the exorcist Masaomi Yaegaki and the High-Class Devil Cleria Belial in order to maintain the status quo that both sides did not want to disturb.

Issei and the rest of the Occult Research club went back to heaven after being contacted by Touji who was transferred there to be cured, he gives Irina the Holy Sword Hauteclere, he has a discussion with Issei alone asking him to take care of Irina. Later during the Qlippoth's sudden invasion on heaven, he fought against Crom Cruach in his True Queen mode, however Issei was overwhelmed by the latter. His fight ended when Crom Cruach walked away, after losing the will to fight due to Walburga interfering with the fight. During the battle Masaomi came in to kill Touji but was saved by Issei, Irina and Xenovia, they were able to defeat him with the use of their Holy swords, and thus freeing him of the Dragon's influence, Masaomi is then killed by Rizevim which infuriates Issei as he had a slight understanding towards him. Issei then proceeded to fight against the latter, however he was overwhelmed by him due to his Sacred Gear Canceler, shortly after Issei was able to use the power of "Penetrate" thanks to Ddraig diving into the depths of the Sacred Gear and recovering a portion of his lost powers, due to his new found power Issei was able to bypass Rizevim's Sacred Gear Canceler and deal Significant damage to him. Right before Rizevim escaped with Lilith, Issei declared that the one to defeat him would be Vali. Later, Issei and Irina went out shopping, She suddenly kisses him and reveals that they've already kissed before as kids. They then meet up with Azazel in a Santa Claus outfit and recall their childhood promise to attack Santa, so with the help of Ophis they charged at Azazel.

In the Extra Life of DX.1, Issei overhears Rias and Ravel discuss about how the Gremory and Phenex Rating Game would've ended if all of Rias current Peerage took part in it, this actually gets everyone interested in finding out which leads Ravel to call Riser for a rematch with Rias which will start on their next holiday. When the Rating Game begins, Issei heads to Gym with Koneko and Xenovia where face against Ile, Nel, Mira and Xuelan. He battles against Mira in his armor and wins by shooting his Dragon Shot which made her naked, before she leaves, Mira ask for his autograph for later. They leave the Gym which was soon destroyed by Akeno and met up with Kiba who goes against Karlamine, as well as Irina who to their surprise fills the place as Riser’s substitute Bishop and faces off with Xenovia. Issei meets up with Ni and Li who want a rematch with him but Koneko, wanting to see specialty in is superior goes against them instead. Isabela, also wanting a rematch with him becomes his opponent, he fires a gigantic Dragon Shot while Isabela dodges it at first, but she is affected by Issei’s Dress Break and retired after being hit by his redirected Dragon Shot.

Issei is soon escorted by Mihae under Risers orders to the new school building where their respected masters are, there they meet up with Asia, Gasper and Rossweisse, Mihae allows him and Asia to pass but fights against Gasper and Rossweisse. They arrive at the rooftop where they see Riser and Rias, Riser requests to fight Issei one-on-one which he also agrees to, they both battle giving everything they’ve got with Issei using his True Queen armour, Riser states that even if he loses to him a hundred times, he is determent to defeat him one day. In the end, the victor goes to Issei and his team. A few days later, Issei again overhears Rias and Ravel discuss Sona’s match with Seekvaira Agares and ask Azazel who would win in a Scramble Flag match between them and Seekvaira which he prepares to call the House of Agares, although Issei is not overwhelmed over the idea.

In Volume 19, Issei and his club members went to Kyoto for New Year’s Day, where he and Rias meets up with Kunou and her mother Yasaka who greet their arrival, although Kunou is upset that Ophis (who she knows as Phis) didn’t come, Issei excuses it that she caught a cold. While Kunou goes to fetch a remedy, Yasaka is glad how close he is with her daughter but asks him to wait until she’s an adult, she teases that until then he can have her instead, at moment Kunou returns and interferes by holding onto Issei’s leg. Issei then learns of Rias previous discussion with Yakasa about Kunou attending middle school at Kuoh Academy in the coming year. Issei heads to the top of the shrine meet up with his friends who’re giving their prayers, although he is embarrassed by Xenovia’s request to have his children this year, stating to be half joking while seeing his expression, her wish is actually have smooth election win or lose and suddenly kisses him for good luck much to his surprise.

At their club room, the group discuss the changes that’s happening around them such Rias and Akeno graduating and how Le Fey and Bennia. Later, Issei watches Xenovia prepare her campaign with help from Irina, Asia and Kiryuu who he shockingly discovers is aware that he and his friends aren’t human. Later that night, in the Hyoudou mansions underground pool, Issei and Rias show off their new technique to members of their club, Vali’s Team, Dulio, Sister Griselda, Tobio and others. He began rubbing sun lotion onto Rias and Akeno, catching the attention of most of the other girls who also want to take turns in him rubbing lotion on them with Ravel sorting a schedule.

The next day, the gang are visited by Vasco Strada, one of the people leading a rebelling against the Church, he Rias a gives a challenge announcing a battle between them and the rebels in three days. Soon Tannin paid a visit to the Hyoudou Residence, asking for their assistance in looking after an egg of a rare species of Spectral Dragon and is surprised to see that Crom Cruach is the one delivering the egg, it’s revealed that he is currently under Tannins care. On the night before the battle, Issei makes final preparation as he meditates to allow energy to wrap itself around his body while in mid-flight above the pool with his Dragon wing, Xenovia entered planning to do her usual routine of skinny-dipping. As they talk, Xenovia expressed her worries of being unable to surpass Sona as the Student Council President and Vasco as the wielder of Durandal. Issei told her that she can do it and asked her why she chose to run as the Student Council President. Xenovia reasoned that she loves Kuoh Academy as it has given a lot to her and she just wants to give something back. Xenovia pulled Issei into the pool with her and kissed him a second time and reminded him of her intent to join his peerage once he becomes a High-class Devil.

On the day of the battle against the Church rebels, they gain assistance from the Sitri group and Brave Saints. They split into two teams to defeat the rebel leaders Vasco Strada and Ewald Cristaldi, Issei tells Kiba who requested to the fight against Ewald to come back alive. Issei and most of the Gremory group along with Saji take part in the battle against Vasco who proves to be a difficult opponent defeat even with the help of Kiba and Irina who had just came over from their previous fight and unmatched by Issei’s True Queen armour. Arthur Pendragon, who has been watching from the side, joins in and actually matches Vasco in a sword fight as everyone watches in awe, however Arthur soon leaves, not knowing why took it as something only swordsman can understand. Xenovia, who receives some insight on Durandal from Vasco, splits Excalibur from Durandal, uses both swords in tandem and defeats him. As Vasco allows himself to be taken prisoner, he’s attacked by the sudden appearance Walburga’s. Everyone readies their stance against Walburga who summons an army of Evil Dragons, however to everyone’s surprise are rendered motionless due to a barrier Rosswiesse set up, her escape route is also cut off by Tobio. Frustrated, Walburga activates her Balance Breaker that manifest the other half of Yamata no Orochi soul from her flames. Everyone gives their best against her with Issei using quickly using Reflect, Penetrate, Bilingual and Dress Break on her while others inflict damage to the Evil Dragon, With Xenovia finishing it off with her new move, Cross Crisis. Walburga froze on the spot witnessing her Balance Breaker destroyed, is then hit by Issei’s Crimson Blaster, resulting in her defeat and arrest.

A few days after the battle, the final day of the candidates in the Student Council Election had begun where Saji and Xenovia won Vice-President and Student Council President repeatedly. Issei met up with Griselda, who came to see the election was moved by her “little sister’s” heartfelt speech, they are joined by Xenovia who is surprise to see Griselda and ask permission to use the Interdimensional room which only angers her. Later The Occult Research Club gathered in the lab where Valerie was and given a piece of the original holy grail given to them by Vasco before his arrest which in turn wakes her from her coma. When everything was going well, the group heard the news of Ravel, who had temporarily joined her Brothers Peerage in a Rating Game against Diehauser, has went missing along with Riser and Diehauser.

In Volume 20, everyone is depressed over the disappearance of Ravel, including Raiser and Diehauser, they believe that Qlippoth is responsible with suspicion of the Champion also being involved. Days later, everyone in Issei’s year have their come to school have a three-way career consultation, he explains to his mother and teacher that he plans on going to Kuoh Academy University and to work under Rias’ father as a carrier choice and then start his own company, which he has not discussed with his parents yet. The next day, Azazel comes to everyone with the news that Ravel and Raiser have been recovered and under Ajuka’s care. The next day, Issei and Asia visit Ophis who is taking care of the Spectre Dragon egg in a vast open space underneath Kuoh Town, sitting slightly away is Crom Cruach in human form who Asia offers some Banana.

As the DxD Team prepare to depart to visit Ajuka, Issei’s dad invites him to go fishing which he declines, Azazel advices him to spend more time with his parents when he gets the chance. They arrive at different dimension resembling a night time beach with two moons where they spot Ajuka next to Ravel who is in a bed barely conscious and assures them that Raiser was sent home safely by Slash Dog’s Team. Ajuka then explains to them about his secret creation from the general public known as the King Pieces and how some top ranked Rating Game contestants have been using them, which was proposed by the higher-ups in the Underworld, a revelation that shocked everyone present. He then explains that while also having one in possession, Diehauser has only ever used his own strength, but reveals the champions involvement in in stealing Agreas in order to pursue the truth of everything, another shocking truth revealed to everyone. Soon Ajuka receives a startling call and tells them to return home as Ophis is being attack by an Evil Dragon.

Back at the Hyoudou Residence, where Ophis is unconscienced on her bed and brutally injured from protecting the Dragon egg from Nidhöggr, further to Issei’s horror finds out that his parents were kidnapped by him. Infuriated, he lashes out at Crom Craunch for not being there in time which Kiba attempts to calm him down. Kuroka and Le Fay came in from the rest of Vali’s Team to bring them info about the location of Agreas, the hideout for Qlippoth’s base. Later on, DxD prepares to strike back as they are teleported to Agreas, with the Gremory team being the main force. As Issei’s group make their way through Agreas to rescue his parents, they come across Nidhöggr, angered at the Dragon who injured Ophis and took his family; Issei activates his True Queen armour. Along with everyone else, they attack Nidhöggr with full force with Issei and Rias using their new technique that grants Rias her on variation of the Scale Mail armour; Crimson Extinct Dragonar. However all their efforts are useless as Nidhöggr recovers from their attacks using several vials of Phoenix Tears, which is until Crom Crauch appears and brutally beats Nidhöggr, allowing Issei and Asia to head to where their parents are with support from all the sword wielders to fend off against any Evil Dragons in their way.

While making their way through the designated building, Issei and Asia hear Diehauser on the monitor and reveals to the public about the truth about the death of his cousin; Cleria Belia, for knowing the existence of the King Piece. They make it to where Diehauser and Rizevim are where Issei and the sudden arrival of Vali face them respectively but are overwhelm by their power, things got more complicated when Rizevim brought Issei’s parents to witness their son in confusion, he then has Diehauser force Issei to drink Dragons blood, turning him more Dragon-like in front of his family who are in shock, especially when Rizevim reveals to them that Issei and his friends are not human. Rizevim mocks and laughs in ridicule towards Issei, calling him a monster in front of his family, he avoids eye contact as he cries and constantly apologises to them, afraid that they might fear and abandon him. Instead they still believe Issei to be their son and accept him as he is, standing up against Rizevim, Issei who is touched by his parents love for him is embraced by them and Asia.

While Issei unintentionally uses Bilingual on his mother’s breasts, he sees through his parents past which shows that they had difficulty giving birth, showing how happy they were when he was born, how worried they became when he was lost from them, as well as all the moments they were there for him. Having regained the will to fight, he battles both Rizevim and Diehauser with his family supporting him; every time he’s knocked down he manages to stand back up, Rizevim attempts to kill his family but are protected by Asia’s awakened Balance Breaker which further irritates him. Issei starts hearing Ophis’ voice who then grants him and Ddraig power, achieving a new form; Diabolos Dragon (DxD), which proves to be immune to Rizevim’s ability and was able to cause him damage. Rizevim tries to heal himself with Pheonix Tears but is betrayed by Diehauser who renders it worthless. They fight outside in mid-air; all of Rizevim’s attacks are proven useless as Issei fires a powerful blast that nearly kills Rizevim, who is now greatly injured before he teleports away. Issei confronts Diehauser over his actions and is slapped by his mother for hurting her children, Issei tells him to atone for his sins as Rias and countless others including himself who want to compete against the Champion, Diehauser asks if Issei saw his cousins soul while in Heaven which he replies the she had a gentle expression, an answer that brought him to tears. Issei starts feeling pain as he coughs blood and collapses on the floor with his family rushing over to him.

In Volume 21, Following his fight against Rizevim, Issei wakes up in the hospital one week later after his previous battle. Issei also loses his ability to speak and think about breasts without feeling pain due to the aftereffects of using DxD mode, which he is warned to never use again. After recuperating enough, Issei saw his parents off and met up with his friends to rejoin the battle against Qlippoth, with an army of different races preparing to face against Apophis heading to the coastal waters of Japan with an impending army of Evil Dragons, Fake Red Dragon Emperor army and one of the Imperial Beasts bodies. After retrieving one the stolen Holy Grail, Issei battles Apophis one-on-one in his True Queen armor within a black barrier and faces difficultly against his Umbrakinesis that dissolves everything it touches and avoids using his DxD mode. Issei lays on the ground injured and barely able to move with both his demonic energy and stamina exhausted, he notices the amulet his mother recently gave him fall off his tattered uniform and inside he finds a photo of him with his parents when he was 3 years old and another of all the current residence at his home. While still in pain, this gives him the will to stand and fight as he begins to recite the forbidden chant.

Issei enters his Diabolos Dragon form and is finally able to inflict damage onto Apophis, as the battle rages on, the two clashes their strongest attacks with Apophis spewing his darkness breath which Issei's overpowers with his Infinity Blaster mixed Longinus Smasher, effectively killing him. Despite so Apophis' black barrier remained, however a luminous horned-humanoid manages to enter, Issei and Ddraig realize that it's the consciousness of Trihexa. Sirzechs then teleports to their location, who had come to fight alongside Issei, they both give it their all to exterminate Trihexa's conscious which keeps on quickly regenerating. Ddraig notices Albion's revelation and decides to unseal his original finishing move for Issei to use; Blazing Inferno of Scorching Flames an ability that allows him to spew flames of intense magnitude. However Trihexa was still able to survive with Issei unable to maintain his form any longer changes back, collapsed onto the ground spewing blood. At the last resort, Sirzechs calls his entire peerage and reveals to Issei that they along some of the other mythology leaders will be sealing Trihexa inside Isolated Barrier Field along with themselves, Issei lays there shocked and awe as he watches them disappear before his eyes and loses consciousness.

Issei wakes up again in a hospital, to his surprise seeing Ophis with a voluptuous figure, Vali who was also hospitalized explains that Ophis adjusted the borrowed power by stabilizing the infinity power within him to a level that his mind and body could withstand, effectively curing him of his Dragon Deficiency and resulting her current state and thus allowing him to see and speak about breasts without pain. Vali also tells Issei about the loss of Azazel, Sirzechs and the others, while he's upset at first, Ophis and Lilith comfort him by saying that they'll always stay with him. Vali also notes that both him and Issei are able to live for a very long time and will await Azazel's return to complain to him.

Powers & Abilities
Demonic Power: Issei has all the powers and abilities common to Devils, including the power to cast spells.
 * Dragon Shot : One of Issei's signature moves. Issei fires a beam of energy by concentrating his magical powers. This move is usually used in tandem with the Boosted Gear to increase its destructive powers. He has also developed a small scale Dragon Shot that is meant for knocking out humans while fending off the members of the Hero Faction who are humans. After his fight with Sirzechs, being inspired by the way he uses his Power of Destruction, Issei starts working on how to redirect his Dragon Shot by moving them in different directions, first using it in Volume 9 against Cao Cao and again in Volume 12 during his battle against Jabberwocky.
 * Issei using Dress Break on Diodara's Peerage.gifDress Break : The second of Issei's signature moves which he uses mainly against females. This move allows Issei to "strip" woman by first coming in contact with them, concentrating his demonic power, then snapping his fingers to activate one of two effects.
 * Ver. B (Body): This move is used to "strip" women by destroying their clothes and/or armor.
 * Ver. A (Astral): This move is used to "strip" women by destroying the effects of spells or abilities that have been used against them.
 * Bilingual : Issei's third signature move. Bilingual gives him the ability to talk to the breasts of all females. It is a helpful technique as it helps Issei learn his opponents' plans and strategies by asking their breasts; however due to complaints from female members from other peerages, Rias banned Issei from using this technique in Rating Games. This move however has a weakness which was shown in the Rating Game between Sairaorg when his bishop Coriana Andrealphus started to strip in front of Issei and instead of telling him battle plans her breast told him what she was going to strip next thus hindering Bilingual.

Flame Blaze: Following his training with Tannin, Issei learned how to use Dragon Flames through Boosted Gear. He first inhale an amount of air to fill his lungs, then uses his demonic powers to produce a small flame in within his stomach and use Boosted Gear's ability to enhance it. While the air mixed the enhanced fire within his stomach, he breath out a large stream of dragon flames from his mouth toward his enemies. He's also shown to widen the range of his dragon flames that can engulf the whole sky as shown his battle against Cao Cao in Volume 12. Because of the training, Issei has also developed a high degree of resistance to fire attacks, so that only the most powerful flames, such as those of a Dragon or the Phenex Clan, can injure him.

Promotion: Being a Pawn, Issei can use promotion to temporarily gain the traits of a Queen, Rook, Knight or Bishop. In Volume 8, after Ajuka Beelzebub rewrote Issei's Evil Pieces, Issei can now use Promotion anytime and anywhere without the King's permission.

Enhanced Stamina: Issei originally possesses average stamina. After being reincarnated into a Devil along with his daily training with Rias, Issei obtains more stamina to use the Boosted Gear. Following his training with Tannin in the Underworld, Issei obtains even more stamina that he could used when in Balance Breaker. He eventually obtains enough stamina to activate his Scale Mail without countdown.

Immense Strength: In the beginning of the series, Issei's strength was considered to be below average compared to others. After his training with Rias and the others in the mountain, Issei when using his Boosted Gear shows that he could go on level with Riser's servant. After his training with Tannin, Issei's strength is further enhanced along with his daily training. His strength is further shown when he fought against Rizevim Lucifer who is a super devil. It is also stated various times in the light novel that his power is equal to that of an Ultimate Class devil. Azazel also stated that out of the young devils that there is only one person who can fight Issei head on that being the former strongest young devil Sairaorg Bael further displaying Issei's strength. After his daily trainings with Kiba, and with the assistance of Sun Wukong himself his strength further enhanced to the point that he can fight Apophis an Evil Dragon that achieved Heavenly Dragon Class.

Immense Durability: Issei was originally very weak and vulnerable, easily hurt by the simplest attack. After his training with Tannin, where he was forced to survive Tannin's continuous assault, Issei's durability greatly improves, along with his daily training further enhanced his durability to the point where his body could withstand continuous usage of the Boosted Gear which he couldn't do so in the beginning. In fact, Issei's durability has been proven several times against opponents like Sairaorg Bael, Cao Cao, Grendel and many others.

Enhanced Speed: Through the use of Promotion, Issei can increase his speed. In his Balance Breaker state, he can use the booster to further increase his speed.

Master Hand-to-hand Combatant: Issei was originally unskilled in fighting but after the training with Koneko and Kiba, Issei manages to obtain basic hand-to-hand combat skills. After his training with Tannin, Issei becomes more skilful in combat, having to learn how to survive Tannin's assault. In fact Issei's prowess in hand-to-hand combat is shown when he went toe-to-toe with Sairaorg Bael, a fellow master martial artist in a fist fight. After his daily training with Kiba and also with Sun Wukong his skills in martial arts greatly improves to the point that he can hold off on his own against Emperor Belial and Rizevim Lucifer who are both also skilled in melee and hand to hand combats.

Dragonification: After sacrificing his left arm, and having it transformed into that of a dragon's in Volume 2, Issei's left arm was immune to damage taken from touching Holy objects. In Volume 14, due to his new body being made from the Great Red's flesh Issei can now freely turn any part of his body into that of a Dragon, by concentrating his thoughts on the specified body part. He first demonstrates the technique by turning his right arm into that of a Dragon in order to combat three Magicians who were sent to attack Kuoh Academy. It is extremely powerful, as shown when he easily breaks through their defense magic and knocks one of them out with a single punch. Issei has also been able to grow Dragon wings from his back. Unfortunately, once the transformation occurs, he is unable to return it to human form, unless he gets the Dragon energy drained from the transformed body part by either Rias or Akeno.

Survival Skills: Because of his training under Tannin, Issei has developed survival skills.

Stealth: Issei has also learned how to mask his presence from people.

Flight: While Issei still lack the ability to fly using his Devil wings, Issei being a former Dragon can fly using his Dragon wings.

Equipment
Boosted Gear : Issei's Sacred Gear and main weapon. The Boosted Gear is one of the 13 Longinus which holds the spirit of the Welsh Dragon, the Red Dragon Emperor, Ddraig, one of the Heavenly Dragons. It is said to have the power to kill a God when fully mastered. Boosted Gear takes the form of a red gauntlet on the wielder's left hand that has the ability to Boost the user's power every 10 seconds without limit, and its sub-ability can Transfer the multiplied power to a being or object, it can even be used on certain parts of the user's body such as the eyes for enhanced vision. Later it gains ability of Penetrate to bypass any defensive abilities (including Rizevim's Sacred Gear Canceller) that would otherwise prevent his attacks from landing, however it does not negate the deactivation of Balance Breaker. Penetrate's effects can also be channeled through other parts of the body, such as the eyes, making it capable to see through anything even women's clothing.
 * Boosted Gear: Scale Mail : The Balance Breaker of Boosted Gear that creates a Red Dragon Armor and Issei's primary battle form. Issei first activated his imperfect version of Scale Mail in Volume 2 by making a pact with Ddraig by giving his left hand to the latter. During his first battle against Vali, Issei used a bracelet given to him by Azazel which allowed him to use the imperfect version of Scale Mail for less than 15 minutes. Issei completed his Balance Breaker during his fight against Kuroka, poking Rias' breast to trigger the evolution. From this point, Issei can Boost without the 10 second limit. At the back of his armor there are two rocket boosters that gives a temporary boost of speed and flight. After the activation of the Juggernaut Drive, Issei's Scale Mail gained a pair of retractable Dragon Wings with pteranodon-like claws that he can use as arms.
 * Boosted Gear: Juggernaut Drive : A form unique to the Boosted Gear and Divine Dividing. The Juggernaut Drive temporarily removes the seal placed on the Heavenly Dragons granting the user immense power. The Juggernaut Drive, however, causes the user to lose sanity while having their lives devoured by the power. Issei indirectly activates an incomplete version of this form when he thought Asia was killed by Shalba Beelzebub with the negative emotion overpowering him thus triggering the Juggernaut Drive. In this form, Issei's speed is greatly increased to the extent that it can be hard for one's sight to follow. This form is also capable of creating Dragon arms and blades from the gems of the armor. It is contains a small cannon within the mouth of the helm that shoots out a laser beam.
 * Longinus Smasher (ロンギヌス・スマッシャー Ronginusu Sumasshā): It's finishing that is the most powerful attack of the Boosted Gear. A launcher appears from the chest of the form that is capable of shooting a powerful energy beam of immense destructive power.


 * Illegal Move Triaina : The Illegal Move Triaina is a specialized technique used by Issei Hyoudou that changes his Scale Mail armor into three different forms based on the Evil Pieces system.
 * Welsh Sonic Boost Knight : Triaina's Knight form. In this form, Issei possesses enormous speed that far surpasses Sairaorg's speed, but to make full use of it, Issei must shed his excess armor, causing it to become thin to the point where it has low defense, making him vulnerable to powerful attacks.
 * Welsh Dragonic Rook : Triaina's Rook Form. In this form, Issei possesses a massive amount of power and defense but has a low body maneuvering speed because of the massive, thickened armor.
 * Solid Impact (ソリッドインパクト, Soriddo Inpakuto): It's respected finishing move that delivers a punch that has its power and speed increased by nailing the percussion hammer located at his elbow.
 * Welsh Blaster Bishop : Triaina's Bishop Form. In this form, Issei possesses an enormous amount of magical energy, which he applies it to the two cannons at the back of his armor.
 * Dragon Blaster (ドラゴンブラスター Doragon Burasutā): It's respected finishing move that is a severely boosted equivalent of his Dragon Shot capable of leveling battlefields and briefly warp space-time. The drawbacks to this is the amount of time it takes to charge the cannons and stamina lost with each shot.
 * Cardinal Crimson Promotion : The Scale Mail's Queen Form that is achieved by gaining the "True Queen". This form changes the color of Issei's Scale Mail armor from red to crimson. Cardinal Crimson Promotion incorporates all three Evil Pieces traits, making it the most balanced and most powerful form of Issei's Scale Mail, having power equivalent or more than the Juggernaut Drive. In this form, Issei is capable of using enhanced versions of the Illegal Move Triaina's abilities. This form, however, is still unstable and requires mastering the three forms of Illegal Move Triaina to stabilize its powers.
 * Solid Impact Booster: By Morphing one of the armors gauntlet into one of the Welsh Dragonic Rook's, it allows it for an enhanced version of Solid Impact. It can also be used in tandem with the Ascalon sword to deal further damage to Dragons.
 * Crimson Blaster: An enhanced version of Welsh Blaster Bishop's "Dragon Blaster" that blasts out a powerful beam from the wings of the armor.
 * Dividing Wyvern Fairy : Originally taking the form of Dividing Gear, a white gauntlet on Issei's right hand which he obtained in his initial battle against Vali in Volume 4. Issei placed one of the jewels on Vali's armor to his, creating the Dividing Gear which allows him to use Albion's dividing powers. This ability, however, reduces Issei's lifespan and thus was banned by Azazel. In Volume 16, Issei is no longer able to use Dividing Gear after gaining a new ability that allows him to create small white Wyverns from the gems of his armor that can not only Divide but can also Reflect incoming attacks. Unlike the Dividing Gear, It only requires Issei's stamina rather than reducing his lifespan. In Volume 17, Issei manages to change the white Wyverns into red at will where they are able to use Ddraig's powers of Boost, Transfer and Penetrate instead. After training with Rias, Issei manages to make use of the red Wyverns to attach themselves on Rias to create her own variation of the Boosted Gear Scale Mail armor called Crimson Extinct Dragonar.
 * Longinus Smasher: In Volume 17, Issei gains access to this ability when the Red Wyverns used Boost on him while in this form. An ability initially available to Juggernaut Drive that from the chest appears a launcher that fires a powerful destructive beam. This however leaves a strong fatigue on Issei as it drains a lot of his stamina and depending how one uses it, it can change the environment. Due to its immense power, this ability has a very long recharge period, lasting at least a month.


 * Diabolos Dragon : This form is the result of Issei borrowing Ophis's power. The armor undergoes further change, as its color changes to be both crimson and black and adding a second set of wings. The power this form grants is so great that it overwhelms Rizevim Livan Lucifer's Sacred Gear Canceler, previously thought impossible. Boost has been changed to D ∞ D as Issei powers up in this form with the ∞ symbol emerging on all of the gems. According to Issei, he was able to use this form because his body was created with Ophis's power and Great Red's flesh. Even so, Issei can only sustain this form for a short period of time, followed by pain that makes death pale in comparison. After the battle against Apophis, Ophis adjust the DxD G, removing the infinity in it, and dub the DxD G as Pseudo Dragon Deitification.
 * Infinity Blaster: A further enhanced version of Crimson Blaster, the wings contain cannons that shoot out a powerful blast of red and black aura that leaves even Rizevim injured to a extent that his body is almost fatally damaged.
 * Longinus Smasher: the form not only is capable of this move, but the blast it shoots out has be enhanced with the power of infinity, delivering further damage, it can also be used in tandem with with the Infinity Blaster.
 * Blazing Inferno of Scorching Flames: An ability that was sealed by the God of the Bible which Issei managed to unlock upon using his DxD form for the second time in Volume 21. Issei releases a powerful breath of fire which can incinerate anything, flames that never go out once ignited as they continue to burn even after being reduced to ashes and can probably burn the soul, until nothing remains. The only existence that was known to be immune to the flames was Albion, Ophis and Great Red.

Ascalon (アスカロン, Asukaron): A Holy Sword given to him by the Archangel Michael after some alterations, Issei was able to wield and merge the sword with his Boosted Gear and keeps it stored inside when not in use. In the anime, Issei is shown to be able to extend the length of the sword. Eventually, Issei has learned how to channel the Dragon Slayer power of Ascalon into his Balance Breaker punches, allowing him to harm Dragons more easily. Later, Issei managed to combine Ascalon's Dragon Slayer ability with his Crimson Blaster.

Quotes

 * "President Rias Gremory's virginity belongs to me!" (Volume 2, Life ∞ vs Power ∞)
 * "Stupidity is fine! If I can't win with ability, I'll excel through stupidity!" (Volume 4, Life 5)
 * "That's because we have to look, if there is an Oppai in front of us!" (Volume 7, Life 2)
 * "I'll never forgive anyone who makes our president cry!" (Season 2 New)
 * (To Irina) "No way, no way in hell. I’ve invested my entire aptitude in magic for this. Would you have me develop a technique that allows me to see through women’s clothing instead? I made such a choice bearing my thoughts, worries and all. I shall...I shall destroy more women’s clothes and then...and then...and then someday, as I gain the ability to destroy them just by looking, I shall continue my fight!" (Season 2 New, Episode 3)
 * (To Irina) "Lechery is my strength! Lechery is my justice!" (Season 2 New, Episode 3)
 * (To Matsuda and Motohama in school) "Boobs are heavier than someone's life." (Season 2 New, Episode 4)

Trivia

 * Issei's height is 170 cm. (5 feet 7 inches) and his weight is 62 kg. (137 lbs.), as stated in the visual book with his data.
 * Issei's birthday is on April 16.
 * Issei's appearance is based off of Kazuma Torisuna from s-CRY-ed because the author is a fan of the series.
 * Issei is a fan of Dragon Ball (Drag-so Ball in the Anime and Manga).
 * In the Light Novel, Issei's Dragon arm is depicted as a scaly Dragon arm that covers his entire left arm, while in the anime, his Dragon arm is replaced by the Boosted Gear.
 * The manga depicts Issei's Dragon arm as a combination of both.
 * Issei has a tokusatsu show in the Underworld called Breast Dragon Emperor Oppai Dragon, which stars him as the main character named Issei Gremory and it is considerably popular among the children.
 * Supposedly, one of Issei's power-ups was to involve sucking Rias' breasts. Unfortunately, that was already too much for Fujimi Shobo, so the author resorted to something else.
 * Four of Issei's eight Pawn pieces have become Mutation Pieces, to represent the powers of Illegal Move Triaina and Cardinal Crimson Promotion.
 * In the short story "25(Twenty Five) at the Clubroom with Rias-buchou!", Issei was stated to have black hair; however, the anime and light novel illustrations portray him as having brown hair.
 * According to the Magicians, Issei's strength is ranked in SS-Class.
 * Issei's life force is currently unreadable due to his body being made from Great Red's flesh and Ophis' powers. At its lowest which is zero it represents "dream" or Great Red and at its highest which is infinite it represents "infinity" or Ophis.
 * His favorite food is cheesecake.
 * Issei Hyoudou has been ranked as number 5 on Watchmojo's Top 10 Male Anime Perverts.