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 brown hair 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
One of the many personality traits that define Issei is his ongoing perverted nature and his obsession with women's breasts. 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, he has attracted the following girls: Rias, Asia, Akeno, Koneko, Xenovia, Irina, and Ravel. This is due to his kindness and unwavering determination of wanting to protect and help those who are important to him despite almost dying by the hands of his opponents. He is, however, oblivious to the feelings of the girls around him (save for Rias), 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 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.

History
Issei is the only child of his family. Not much is shown on his past, except for the fact that he is a childhood friend of Irina Shidou. 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 inadvertably 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 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 is too late when Raynare takes Asia's Twilight Healing, killing her. Determined to avenge Asia's death, Issei fights Raynare in a one-on-one duel and defeats her after activating his true Sacred Gear, the Longinus, Boosted Gear. 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.

At the beginning of Volume 2 after his daily training with Rias, Issei was shocked to learn from her that Asia will be moving in with him and transferring to Kuoh Academy. Issei later 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, Sirzechs' Queen, 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 assisted in defeating half of Riser's Peerage before going off to face Riser. Issei, however, was incapable of doing anything as his body has 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. 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 in 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.

Birth of the Breast Dragon Emperor
In Volume 3, Issei was 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. He later reencounters his childhood friend, Irina Shidou, who was under the Church's orders to retrieve the stolen Excalibur swords. He also found out about Yuuto's past and decided 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 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.

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, adding with the Holy Lightning of Baraqiel and Akeno and allowing them to defeat Loki.

In the Extra Life of Volume 8, Issei and Rias went the Underworld and underwent an engagement ceremony at the Ruins of Connection. Issei, however, does not realize the purpose of the ceremony. 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, Issei and Rias were tested on table manners; and in the third trial, Issei and Rias was tested 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 goes to Kyoto for their school trip. While on the train to Kyoto, 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 untaps his potential and the possibilities of the Boosted Gear. 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 Trident due to his desire to protect his friends and Rias' breasts, allowing him to change the Scale Mail armor through Promotion. With the newfound power, Issei manages to temporarily overwhelm the entire Hero Faction before succumbing to the exhaustion caused by Illegal Move Trident. 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, allowing 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 "Buchou", 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 by her, made him afraid to call girls by their first name, and also made him 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. 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 goes 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 killed Shalba. 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 gains another body with the help of the Great Red and Ophis. He returns and sucessfully 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 outmached 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 it does not work because Truth Idea's 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 go on dates with Issei as well.

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.

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 Galnstein 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 disposed of 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 in which Issei happily agreed to.

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.

Powers & Abilities
Dragon Shot (魔力弾（ドラゴンショット）, Doragon Shotto): 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.

Dress Break (洋服崩壊（ドレス・ブレイク）, Doresu Bureiku): The second of Issei's signature move which he uses mainly against females. This moves allows him to strip a female's clothes after coming in contact with them by concentrating his magical energy on the clothes.

Bilingual (乳語翻訳（バイリンガル）, Bairingaru): 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 fighters, Rias banned Issei from using this technique in Rating Games

Dragon Flames: Following his training with Tannin, Issei learned how to use Dragon Flames, Tannin's signature attack. He is also  able to shoot flames from his mouth. 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.

Enhanced 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,

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.

Expert 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 master martial artist in a fist fight.

Dragonification: After sacrificing his left arm, and having it transformed into a Dragon arm in Volume 2, Issei's left arm was immune to damage taken from touching Holy objects. In Volume 14, it is revealed that 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. 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 gained a minor survival expertise while in mountainous regions.

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

Demonic Power: Issei has all the powers and abilities common to Devils, including the power to cast spells. However he possess little Demonic Power and has little talent in the manipulation of it.

Equipment
Boosted Gear (赤龍帝の籠手（ブーステッド･ギア）, Būsuteddo Gia): Issei's Sacred Gear and main weapon. The Boosted Gear is one of the 13 Longinus where one of the Heavenly Dragons, Ddraig, the Red Dragon Emperor, resides. It is said to have the power to kill a God when fully mastered. His Sacred Gear ability is to double his power every 10 seconds without limit, and his sub-ability can transfer the multiplied power to a being or object.
 * Boosted Gear Scale Mail (赤龍帝の鎧（ブーステッド・ギア・スケイルメイル）, Būsuteddo Gia : Sukeiru Meiru): The Balance Breaker of Boosted Gear 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 Dragon. 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. After the activation of the Juggernaut Drive, Issei's Scale Mail gained a pair of Dragon Wings but Issei himself is still inexperience in flying and leaves it to Ddraig.
 * Dividing Gear (白龍皇の籠手（ディバイディング・ギア） Dibaidingu Gia): In his initial battle against Vali in Volume 4, Issei placed one of the Jewels of the latter's Divine Dividing on his Scale Mail armor, 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.
 * Dividing Wyvern Fairly: In his battle against Euclid in Volume 16, Issei gained a new ability to create small white dragons from the gems of his dragon armor that can not only divide but can also reflect incoming attacks. Unlike the Dividing Gear, this does not reduce Issei's lifespan.
 * Juggernaut Drive (覇龍（ジャガーノート・ドライヴ）, Jagānōto Doraivu): An ability 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 are devoured by the power. Issei indirectly activates this form when he thought Asia was killed by Shalba Beelzebub with the negative emotion overpowering him thus triggering the Juggernaut Drive.
 * Illegal Move Trident (赤龍帝の三叉成駒（イリーガル・ムーブ・トリアイナ）, Irīgaru Mūbu Toriaina): The Illegal Move Trident 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 (龍星の騎士（ウェルシュ・ソニックブースト・ナイト）, Werushu Sonikku Būsuto Naito): Trident'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 (龍剛の戦車（ウェルシュ・ドラゴニック・ルーク）, Werushu Doragonikku Rūku): Trident's Rook Form. In this form, Issei possesses massive power and defense but has a low body maneuvering speed because of the massive, thickened armor. Its finishing move is "Solid Impact" (ソリッドインパクト, Soriddo Inpakuto), a punch that has its power and speed increased by nailing the percussion hammer located at his elbow.
 * Welsh Blaster Bishop (龍牙の僧侶（ウェルシュ・ブラスター・ビショップ）, Werushu Burasutā Bishoppu): Trident'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. Its finishing move is "Dragon Blaster" (ドラゴンブラスター Doragon Burasutā), 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 (真紅の赫龍帝（カーディナル・クリムゾン・プロモーション）, Kādinaru Kurimuzon Puromōshon): 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. This form, however, is still unstable and requires mastering the three forms of Illegal Move Trident to stabilize its powers.

Ascalon: Given to him by the Archangel Michael after some alterations, Issei was able to merge the sword with his Boosted Gear and keeps it stored inside when not in use. 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. Issei rarely uses the Ascalon in battle, mostly handing it to Xenovia.

Familiar
In Volume 13, Issei is given a familiar, the living Norse flying ship Skíðblaðnir, by Surtr Second. Although it is presently only the size of a toy boat, according to Mathers, it will continue to grow and evolve into different forms by using the aura and imagination of its master as its source, potentially even becoming its own dimension. Second also jokes that if Issei is going to become a harem king, he needs a harem palace. With Issei as its master, it might grow into a flying harem palace. He later names it Ryuuteimaru in Volume 14. Issei can use Ryuuteimaru to fly around as he has yet to learn how to fly using his Devil wings.

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)

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 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).
 * In the Light Novels and Manga, Issei activated his Boosted Gear in the Occult Research Club whereas in the anime, he activated his Boosted Gear during Kalawarner's attack.
 * 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. As of Season 2, the anime version of Issei's Dragon arm resembles how it is described in the Light Novel.
 * 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 (乳龍帝おっぱいドラゴン Chichiryūtei Oppai Doragon), which stars him as the main character named Issei Gremory and it is considerably popular among the children.
 * Issei has become rather embarrassed by the Oppai Dragon theme song, and how popular it has become. Especially since a line from it was the last words from the previous Boosted Gear hosts to him, and the only words spoken by Great Red to him directly.
 * Issei earns a percentage of the revenue from the Oppai Dragon series, because of publishing rights and other reasons.
 * The amount of money that he earns is enough to shock him.
 * Grayfia is, at present, managing his money for him.
 * 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 Trident 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 is the only person other than Sirzechs to see Grayfia's naked body and the only one to see Sona in a swimsuit beside her family.
 * 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" and at its highest which is infinity it represents "infinite".