|“||I’m going to become a Harem-King!||”|
– Issei Hyoudou shouting out his dreams, Volume 1, Life 2
Issei Hyoudou is the main male protagonist of High School DxD. He is a third-year high school student at Kuoh Academy in Class 3-B 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 at 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. He has achieved his goal of becoming a High-Class Devil, obtaining his own servants, and is one step closer to owning a harem, becoming a "Harem King".
Issei is a 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.
He has been said to show manly expressions by his paternal grandmother. Issei's height is 170 cm (5 feet 7 inches) and body weight is 62→65 kg (137→140 lbs.).
Issei is initially 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 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 into other people's business" as he helped Yuuto Kiba, Koneko Toujou, and Akeno Himejima overcome their fears 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. He has a habit as mentioned by his mother of not forgiving himself if he does something wrong: always saying sorry if said thing is mentioned, and showing an expression of pain and regret.
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 the knowledge that the girls do have romantic affection for him, he still has problems acknowledging some of their ongoing rivalries, an example being who gets 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.
Before Issei's birth, his mother became pregnant twice, but the pregnancies ended in miscarriages. So when Issei's mother got pregnant for the third time, his father had paced back and forth in front of a Shinto shrine honestly wishing that this time they would succeed. When the newborn was finally born he was named Issei, meaning "honesty", for his father's honest prayers.
He is a childhood friend of Irina Shidou and they would always play together back when she still lived in the neighborhood, although he thought she was a boy at the time as he vaguely remembers her. A few times Issei was invited to go to church with her family. On occasions they would stay over at each other's houses, one of these visits when Issei slept over at Irina's, she kissed him while he was sleeping. Eventually, Irina moved to England due to her father's job.
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.
Powers & Abilities
Demonic Power: Issei has all the powers and abilities common to Devils, including the power to cast spells. His demonic power was originally lower than a child's, unable to travel via magic circles but now he has sufficient power to do so. By True Volume 2, he can create a teleportation magic circle. Through the use of Promotion, Issei can increase his demonic power. In Volume 14, Issei can summon Ryuuteimaru and in Volume 25 Issei can use magic communication circles.
- Dragon Shot (魔力弾, 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. In his Balance Breaker state, he can fire his Dragon Shot without increasing its destructive power. 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.
- Flame Blaze: Following his training with Tannin, Issei learned how to use Dragon Flames through Boosted Gear. He first inhales 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 breathed 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.
- Dress Break (洋服崩壊, Doresu Bureiku): The second of Issei's signature moves which he uses mainly against females. This move allows Issei to "strip" women 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.
- Pailingual (乳語翻訳, Pairingaru): Issei's third signature move. Pailingual 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 Pailingual. In True Vol 1, Issei can combine penetrate with Pailingual to talk to powerful being breast and in his Diabolos Dragon form, Pailingual pink space covered the whole island.
- Pai-Phone: Is a variant of Pailingual, using women's breasts Issei is able to communicate through breasts to other women's breasts.
- Nyuutron Beam Cannon: Issei's fourth signature move. Nyuutron Beam Cannon gives Issei the ability to attach his Scale Mail's tail to a woman's breast and absorb their breast energy. This allows a powerful beam cannon to be fired as the result of breast energy being infused with Issei's demonic power. The color of his beam is pink in comparison to his previous abilities. The woman's bust size is displayed in his gauntlet's jewel and the number determines how powerful the beam will be. By using Rosswiesse's breast, which size is 96, he was able to launch an attack comparable with Infinity Blaster. It is very powerful, as it was able to defeat the strongest Grim Reaper, Thanatos.
Immense Strength: At the beginning of the series, Issei's strength was considered 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 a 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, 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 and that is the former strongest young devil, Sairaorg Bael, further displaying Issei's strength. After his daily training 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 using his Diabolos Dragon God. In Volume 24, Issei was able to keep up with Thanatos who The Strongest Grim Reaper. In Volume, 25 Issei can fight on par with Vidar in his Ragnarök Earth Berserk.
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 skillful 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 fistfight. 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 Diehauser Belial and Rizevim Lucifer who are both also skilled in melee and hand to hand combats. In Volume 22, Issei in Cardinal Crimson Promotion is able to fight on par against Baraqiel who fusing it into punches and kicks with Holy Lightning. In Volume, 25 Issei went toe-to-toe with Vidar who his excellent powerful kicking techniques. Issei can also combine boost power from Boosted Gear and dragon aura increases the power of his physical attacks.
Promotion: Being a Pawn, Issei can use the 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.
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.
Immense Durability: Issei was originally very weak and vulnerable, easily hurt by the simplest attack. Through the use of Promotion, he can increase his defense. 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. In Volume 22, Issei can endure Baraqiel holy lightning and continuing to fight despite the intense pain. In Volume, 25 Issei can withstand Vidar in his Ragnarök Earth Berserk signature move, with the impact crashed onto Yggdrasil.
Immense 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. In Volume 20, in his Diabolos Dragon form, he was able to appear in front of Rizevim before he can react. He was able to keep up with Vidar in his Ragnarök Earth Berserk.
Immense 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 use when in Balance Breaker. He eventually obtains enough stamina to activate his Scale Mail without a countdown. In Volume 23, he was able to keep fighting at his best throughout the whole two-hour Rampage Ball Rating Game.
Skilled Tactician: Although he is often outsmarted and considered an idiot, he is proven himself to be a slight skillful tactician. In Volume 9, he acts as a leader and a tactical fighter, where he uses his brain to fight properly the Hero-faction. Issei claims that his skills are not that enough, but Kiba mentioned that if it is not for his orders they couldn't fight and defend themselves from the sudden attacks of the Hero-faction.
Survival Skills: Because of his training under Tannin, Issei has developed survival skills.
Swordsmanship: While Issei is not proficient in wielding a sword like Kiba or Xenovia, he has learned the basics of swordsmanship from Kiba and his sword skills improve in their training sessions together.
Stealth: Issei has also learned how to mask his presence from people.
Flight: While Issei still lacks the ability to fly using his Devil wings, Issei being a former Dragon can fly using his Dragon wings.
EquipmentBoosted Gear (赤龍帝の籠手, Būsuteddo Gia): 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 focused on certain parts of the user's body such as the eyes for enhanced vision. Issei can use Boosted Gear to strengthen his physical abilities and demonic power. Later it gains the ability of Penetrate to bypass any defensive abilities (including Rizevim's Sacred Gear Canceler) 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 any part of the body, such as the eyes, making it capable of seeing through anything, even women's clothing.
- Boosted Gear: Scale Mail (赤龍帝の鎧, Būsuteddo Gia: Sukeiru Meiru): 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 and it strengthens his powers and abilities. At the back of his armor, there are two rocket boosters that give 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 (覇龍, Būsuteddo Gia: Jagānōto Doraivu): 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 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 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 (赤龍帝の三叉成駒, Irīgaru Mūbu Toriaina): 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 (龍星の騎士, Werushu Sonikku Būsuto Naito): 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 (龍剛の戦車, Werushu Doragonikku Rūku): 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 (龍牙の僧侶, Werushu Burasutā Bishoppu): 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 that 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, 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. 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. In Volume 22, it is revealed that Issei can enter True Queen without having to chant, and due to Diabolos Dragon God mode, its power has been increased.
- Solid Impact Booster: By morphing one of the armor's gauntlets into Welsh Dragonic Rook's, it allows it for an enhanced version of Solid Impact. It can also be used in tandem with Ascalon to deal further damage to Dragons.
- Crimson Blaster: An enhanced version of Welsh Blaster Bishop's "Dragon Blaster" that shoots a powerful beam from the wings of the armor.
- Dividing Wyvern Fairy (白龍皇の妖精達, Dibaidingu Waibān Fearī): Originally taking the form of Dividing Gear (白龍皇の籠手, Dibaidingu Gia), 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 him, 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 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 (深紅の滅殺龍姫, Kurimuzon Ekusutinkuto Doragunā). Issei also made use of the red Wyverns to attach themselves on Xenovia to create her own variation of the Scale Mail armor called Crimson Destruction 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 powerfully destructive beam. This, however, leaves strong fatigue on Issei as it drains a lot of his stamina and depending on 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 God (龍神化－『D×D』・G－, Diaborosu Doragon Goddo): 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 grant 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 adjusted DxD into DxD G, removing the infinity in it and dubbing the form Pseudo-Dragon Deification. The form can only be maintained for three minutes at most, with the time limit becoming shorter by attacking or defending to the point it can last only ten seconds. In Volume 23, Issei reveals the ability to perform a partial Pseudo-Dragon Deification on his left arm, allowing him to use his Dragon God Aura to a lesser extent with less stamina consumption. With this technique, Issei can combine his Dragon God aura into both Solid Impact Booster and Dragon Shot. In Volume 25, after drinking the miracle drug Amrita, Issei can maintain his Pseudo-DxD form for 88 minutes in combat.
- 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 an extent that his body is almost fatally damaged. By using it, DxD G's time limit of three minutes is cut down to ten seconds.
- Longinus Smasher: The form is not only capable of this move, but the blast it shoots out has been enhanced with the power of infinity, delivering further damage. It can also be used in tandem with the Infinity Blaster, fusing the two blasts into an even more powerful attack.
- 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 existences known to be immune to these flames are Albion, Ophis, and Great Red. Its area of effect can cover an entire island.
- Dress Break DxD: By using his Dragon God aura, Issei can increase his range that halts a female target’s movement, and by strengthening his left hand he can destroy their clothes without even touching them.
- Ddraig Manifestation: Due to drinking the miracle drug Amrita, Issei gained the ability to summon Ddraig into battle after the  countdown on the right gauntlet reaches zero.
- Welsh Dragon Flare: A combination technique between Issei and Ddraig, both attack simultaneously with Issei unleashing Infinity Blaster and Ddraig use his dragon breath, which the aftershock leaves the whole area painted in crimson.
Ascalon II (アスカロンII, Asukaron II): The second version of Ascalon. A long sword that releases holy aura, but is more of a dragon sword rather than a Holy Sword. Issei keeps this sword within his right gauntlet that was free.
- "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)
- Issei's birthday is on April 16.
- Issei's appearance is based on 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 (乳龍帝お, Chichiryūtei Oppai Doragon), 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.
- 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's name means "Sincere/Honest".
- His surname means "Soldier" in reference to him being a Pawn, as pawns are considered to be foot soldiers in chess analogy. So his full name means "Sincere or honest soldier".
- Issei shares the meaning of the series' title that refers to Great Red: "Dragon of Dragons" as he can be considered a mini Great Red, who the title mainly refers to.
- In addition, he along with Vali have made another meaning for the title that refers to themselves: "Diabolos (Devil) Dragon".
- His first kiss was with his childhood friend Irina Shidou, albeit he was asleep.
- Issei is the only man in existence to have seen Gabriel in a bikini, as well as the most beautiful women in all of Heaven who serves under her; in an old school swimsuit, transparent negligee, and athletic clothing.
- Issei's first ever meeting with Asia may have been foreshadowing to the relationship between Cleria Belial and Masaomi Yaegaki, as at first, Issei and Asia similarly to Cleria and Masaomi, were forbidden from seeing each other in the same town; Kuoh Town due to the Devil's side and Angel's side still at feuds with each other.
- Issei was originally envisioned with Kiba's character traits but later changed into a pervert because Ishibumi felt those character types were too "weak" for the main character.
- Issei was originally going to be just a human who helps Asia.
- Despite not officially being a member of the Gremory clan yet, he is already considered one by the members (minus Rias) and their servants.
- Issei makes review videos for Oppai Dragon products while acting as the "Oppai Dragon" himself and uploads them to DeviTube. This caused the merchandises' sales to increase.
- According to Ophis's spawn Lilith, Issei smells like her, Ophis, and Great Red.
- According to Elmenhilde, Issei's blood tastes sweet, mellow, and rich, and is absolutely addictive.
- In the English dub, Issei’s nickname Oppai Dragon is Grabbin Dragon.
- Issei, in reality, is the third child. With two miscarriages suffered by his mother, he is the only surviving child of his parents and he has two older siblings who were never born.
- In Volume 25, Issei is very popular in Norse mythology as many people in Valhalla were cheering for him.
- Issei has broken off all the engagements of the female characters placed into one, (Rias, Kiyome, and Rossweisse) all of which have fallen in love with him as a result.
- As revealed in a short story, Issei is very good at giving massages, so much so that it's too erotic for women.
- His Japanese voice actor, Yūki Kaji, eventually married Ayana Taketatsu, the Japanese voice actress of Koneko, on June 22, 2019.