"Are you serious! I'm able to make my own harem? I could have sex with them as well right?" "Yes. I think it's fine if it’s with your servants." I felt a shock going through my body. This is absurd! Something like that is actually possible? In the real world and also as a human, it is really hard to build your own harem. If I was still an ordinary human, no matter what I'd do, I won't be able to get a batch of girls since right now I'm in a bad position. I don't even have a single girlfriend. Well I did, but I was killedby my ex. But now! Now I can...! "Oooohhhh yeaaah!! Being a devil rocks! Hell yeah! I can't calm myself anymore! I probably can throw away my porn!"
Remember your first date and how much it sucked, what with nervousness, lack of ideas as to what to do, and running late when you thought you came in early? Well, Issei Hyodo has you beat. Okay, his first date started out well enough — in fact, 99% of it was awesome. It's just that the other 1% involved his girlfriend stabbing him in the stomach and leaving him to bleed to death.Enter Rias Gremory, his school's beautiful, crimson-haired sweetheart. She's also a demon queen, who resurrects him. Without knowing what became of him, Issei returns to his normal life of watching porn, peeking into changing rooms and interacting with his two fellow perverts. But no sooner had he started reconnecting to his old life than a fallen angel attacks him, only to be saved once more by Rias — now accompanied by two of her faithful servants, Akeno Himejima and Koneko Toujou.The next day he wakes up naked, right next to an equally naked Rias, who then tells him that she has saved him by turning him into a demon, and is now under her employ. With a promise of power, glory and his very own harem, Issei doesn't mind the tradeoff and quickly jumps onto the prospect. To this end he joins the Occult Research Club, consisting of himself, Rias, Akeno and Koneko, as well as Asia Argento, a girl raised in a church, and Yuuto Kiba, the school's charismatic prettyboy.Mix Black Butler, xxxHOLiC and Tenchi Muyo! with American Pie and To Love-Ru, add in some Scott Pilgrim and you get this hilarious, sexy and compelling series.An ongoing 2008 Light Novel series by Ichiei Ishibumi and illustrated by Miyama-Zero, High School DxD is a series that runs away with all the gratuitous fanservice and one boy's slow ascent up the ranks of the demon world. It also has an ongoing 2011 manga series illustrated by Hiroji Mishima and a Winter 2012 Anime adaptation. A second season aired as a part of the Summer 2013 Anime season and a third season got the green light in June 2014.There is also a Lighter and SofterSpin-Off of this series, starring Asia and Koneko called High School DxD: Asia and Koneko's Secret Contracts.Funimation also has licensed the anime. You can watch it here at Funimation or here at Nico Douga. They're censored though.Two licensed games have also been made, one for the Nintendo 3DS, based on the anime's first season (which is unfortunately not released overseas), and one (currently in development) for the Playstation Vita, instead based on the anime's second season.The series is decidedly NOT about high-schoolers playing Dungeons & Dragons. Also not to be confused with So I Cant Play H, which started airing an anime around the same time with a similar red-haired Magical Girlfriend. Frequently mistaken for, but unrelated to, the similar-sounding-named High School Of The Dead.
The Occult Research Tropes:
Accidental Pervert: Generally there's nothing accidental about the situations Issei gets caught in, but that time his mom found him sleeping naked next to Rias was totally innocent.
Also, when the girl's kendo team catches him next to a hole in the wall of the girl's changing room, he actually hadn't been peeping. Not that he didn't want to, though.
Action Girl: So far, almost all female devils (except Asia) are pretty good at ass-kicking anyone with either physical or magical attacks.
Special mention goes to Leviathan (levi-tan). When the Underworld was attacked, she refused to be cowed by the threat of the god-slaying spear and confronted one of the Bandersnatch herself.
Becomes a plot point in the first OVA. A demon creates a plant that gives girls big breasts. Issei, being the pervert that he is, actually tries standing up for the monster, thinking that maybe big breasts aren't all bad. Koneko, on the other hand, has a huge Battle Aura, and has a gigantic tree trunk over her head, ready to take that thing out.
All Men Are Perverts: We start with Issei of course, but he's definitely not the most perverted guy ever. The only male character who doesn't seem to even be remotely close as a pervert is ironically Vali, his rival.
Badass Family: The Gremory family. When you've got the Crimson-Haired Ruin Princess (Rias), the Silver-Haired Queen of Devourer (Grayfia), and the Brunette Madame the Extinct (Lady Gremory) gunning after you, you might wanna run away pretty fast.
Badass Normal: Sairaorg lacks any special power but trained his body hard enough that he can defeat any of the devils in his generation with ease. Only Issei can stand up to him among the new generation of devils.
Barbie Doll Anatomy: In the anime's opening the girls (most noticeably Asia) have nipples but the crotches of barbie dolls, but early in the manga even Issei lacks nipples, though in the manga the girls use Godiva Hair too.
Big Fancy House: Rias' house in the Underworld and later on, Issei's house becomes this.
Bishōnen: Issei, Kiba, Sairaorg, Vali, Cao Cao... Many of the boys in the series are quite nice-looking.
Bishoujo: All of the main girls and most of the supporting ones are attractive women.
Boobs of Steel: Averted, at least as far as the Occult Research Club goes. Rias and Akeno are primarily magic users, and the club's strongest physical fighters are Xenovia (around the median) and Koneko (the flattest).
Book Ends: The anime starts and ends with the same scenes, with slight differences.
Boss Rush: The entirety of volume 16 pits the group against: Grendel, Crom Cruach, Rizevim, and Euclid.
Breather Episode: Episode 7 of season 2 is a fairly lighthearted pool episode, following some rather brutal fighting from the previous one.
Brick Joke: Sirzechs' suggestion to Issei to use Gift on Rias' breasts in Volume 4. Seven volumes later, it shows Issei replenishing his aura at the cost of Rias' breasts shrinking.
Bunny-Ears Lawyer: Anybody who is in the high ranks are this. Sirzechs, Serafall, Azazel, Odin.. take your pick.
Butt Monkey: Compare everyone in the Occult Research Club and Issei. A good amount of the time Issei is going to take the brunt of some damage from events like sports, rumors, or from Azazel's crazy experiments.
Can't Catch Up: Beginning to show shades of this in the light novels in regards to the other members compared to Issei and Kiba, but especially Issei. They both start off as relatively weak members of the Occult Club with Issei being by far the weakest and Kiba being only around Koneko's level at best. Rias and Akeno at this point were far stronger. Then Kiba and Issei master Balance Breaker and everyone is left coughing in the dust. This is best exemplified when Issei was able to beat Sairaorg Bael using his Balance Breaker where as Kiba, Xenovia and Rossweisse (the three strongest in the Occult Club with Kiba being by far the stronger of the three) only managed to cut off an arm of Sairaorg without Balance Breaker and the rest likely couldn't even scratch him. Right now, Issei is by far the strongest member of the Occult Research Club, with Kiba just behind.
Can't Have Sex, Ever: It's actually a requirement by the publishers, otherwise we can pretty safely assume this series would've gone in a whole other direction by now.
An in-universe example with Koneko. As a Nekoshou, Koneko can bear children even at her age. If she did, both she and the child would likely die. Issei tells her they should wait, and she agrees.
Cat Girl: They exist in the universe. Koneko is one.
Chainsaw Good: Riser's two pawns, who are also twins, uses this against Issei.
Chess Motifs: The very nature of the Ratings Games, where players in a team are designated either as King, Queen, Bishop, Rook, Knight or Pawn. Within the Occult Research Team, Rias is the King, Akeno as the Queen, Kiba and Xenovia as Knights, Asia and Gasper as Bishops (with Ravel as a free agent from Raiser's team), Koneko and Rossweisse as Rooks, and Issei using up all of Rias' eight Pawn pieces.
Tarot Motifs: Meanwhile, the angelic bureaucracy has this going on — or to be exact, its playing-card equivalent, as evidenced by Irina being assigned as the Ace of Spades, with the Archangels Michael, Gabriel, Raphael and Uriel designated to the suits of Spades, Hearts, Clubs and Diamonds, respectively.
Chekhov's Gun: Asia showing the holy water to the club room proves instrumental to Issei when he needed to defeat Riser.
Back in Volume 4, Issei absorbed some of Vali's powers by infusing a part of the White Dragon Emperor's shard in him, thus being able to use Divine Dividing with only a Million to One Chance of it working.
In Volume 10, while Issei's almost about to lose consciousness, one of the past White Dragon Emperors appeared to him and told him to never give up and used its halving abilities to make the remnants of the past Red Dragon Emperors lose their grip on Issei. He then gets to use Illegal Trident Cardinal Crimson Queen.
Now in Volume 16, Issei and Ddraig figure out a new more permanent use for the White Dragon Emperor's power, making lots of small white dragon statuettes that float around him, reflecting and dividing the power of enemy attacks (Possibly only working during the previously mentioned Cardinal Crimson Queen).
Chekhov's Gunman: Quite a few in this series that were mentioned at best make an appearance:
Back in volume 1, Asia's past reveals that she healed a devil and that she was exiled from the church. Five volumes later, that same devil reappears in front of Asia and turns out he planned the entire thing because he wanted to break down Asia.
Volume 4 has Akeno alluding that she's a half-Fallen Angel half-devil and that she can never forgive her father. Three volumes later, he makes an appearance. They finally get to resolve their issues too.
Come to think of it, Gasper is technically one too by Rias alluding that she used her first Bishop piece already back at the end of the first volume.
Volume 10 has a boy who couldn't make it into the autograph event and that Issei was able to sign an autograph for him back stage and told him to not cry at all. At the climax of his and Sairaorg's match, that same kid encouraged the other kids that Oppai Dragon will never give up, thus kids reaching out to him and not give in to Juggernaut Drive.
Chick Magnet: Not so much in the beginning Issei, but after being reborn...so many hot women are after him.
Power is Sexy: According to Ddraig, anybody who possesses the power of dragons instantly becomes a Chick Magnet because of this trope. He even describes to Issei that one of his past users slept with a lot of women.
The Chosen Many: For something to be so rare, there sure are a lot of Sacred Gear users in the setting. That's not counting according to Word of God, the thirteen Longinus users, one of which being Issei's Boosted Gear.
Church Militant: It seems the church in this setting has special squads of assassins and exorcists to deal with the supernatural.
Clothing Damage: When Issei first gets his powers in the anime, the Fallen Angel that's attacking him gets what little clothes she's wearing blown off. And then he gets Dress Break, the ultimate move in a Rating Game where it outright got banned after the first game was over. Needless to say we deified Issei for this trope.
Clingy Jealous Girl: Asia shows signs of it in volume 3, Rias as well. Then...Xenovia, Akeno, Irina, and Koneko just slightly.
The "clingy" part gets turned Up to Eleven in volume 14, and it is adorable.
Competitive Balance: The Rating Games have this format. Take note however that depending on the individual this could change. For example giving someone fast a Rook would make them a Lightning Bruiser instead.
Crazy-Prepared: Issei's fight against Phenex is nothing but this. Armed with the cross and holy water while having your left arm become dragon-like (which then won't harm Issei) against a guy who can regenerate wounds? Yeah.
Cross Counter: Him and Riser in the final fight of Volume 2. This is also the part where Issei shows he can be Crazy-Prepared when the situation calls for it.
Crouching Moron, Hidden Badass: Issei, of course. Most of the time, he just acts like a horny teen with nothing on his mind but boobs - his main 'ambition' is to have his own Harem, and he tends to dramatically proclaim his next 'target'... such as "sucking on Rias-sempai's breasts!" Even after he becomes a Devil, he's still just a 'pawn', he's terrible at making Pacts with mortals, and can't even use the Magic Circles to travel unaided. However... when he's forced to fight, particularly in defense of the girls he cares about, he can and will kick epic amounts of ass. And yet he continues to have little self-confidence, failing to realize how impressive he looks from the outside. In an unusual twist on this trope, however, he's actually at his most badass when the two sides of his personality are in balance, since he can literally draw destructive power from his lust.
Issei's first fight against Riser. Although he tries to be the Determinator, Riser continually beats him to the point that Rias surrenders the rating game to save his life. Issei then returns the favor in their next fight.
Issei and Kiba vs Xenovia and Irina. The latter two win rather easily, largely due to faults the former two had, such as Kiba attempting to use a big, heavy sword which negated his speed advantage, and in Issei's case, Koneko warning Irina about his Dress Breaker ability ahead of time.
Cute Bruiser: Koneko is adorable enough to be considered a school mascot, and strong enough to punch you through walls.
Damned by Faint Praise: In episode 7, Koneko tells Issei that embroidering some headbands is "A feat out side of my expectations".
Dancing Theme: The anime ending theme. Ye gods, the ending theme!
Dark and Troubled Past: Who knew..Everyone in Rias' group except Issei has this. Rias is the head of her household since her brother became the de facto ruler of hell, Kiba was a survivor of an illegal church experiment in which only he survived because of Rias, Koneko was saved from death after her sister killed her master, Akeno is a half-Fallen Angel due to her father being one and her mother a human. Her mother was killed by her father's enemies. Asia has the ability to heal anything, at first the church thought it was a blessing until they found her she could also heal devils, after which they branded her a witch.
Darkest Hour: Volume 11. To wit, Hades starts a war in Hell, 75% of Ophis' power was taken from her thus unable to return to her dimension, Vali is poisoned thanks to Samael the Dragon Eater, Issei dies, and everyone else is having a Heroic BSOD.
A Day in the Limelight: More like a volume in the limelight but everyone in the Occult Research Club has their stories centered on a certain volume. Issei and Asia for Volume 1, Rias for Volume 2, Kiba for Volume 3, Gasper for Volume 4, Koneko for Volume 5, Asia again for Volume 6, Akeno for Volume 7, and Ravel for Volume 14.
Death Is Cheap: Otherwise the series probably would've ended right away.
Declaration of Protection: Subverted with Asia in episode 3. Issei does try to protect her, but he's nowhere near strong enough to fight Freed, and only manages to land one lucky punch. Issei even suspected he was outmatched, and were it not for the timely arrival of Rias, he probably would've died there.
Played gloriously straight in Volume 6, where both Issei and Xenovia swear that if Diodora ever comes near Asia again, they will tear him limb form limb.
Defeat by Modesty: Issei's Dress Break invokes this, sure its mainly used on females but usually it's not modesty that defeats them, it's the heavy-handed blasting coming from Issei or one of his teammates as person in question covers their naughty bits.
Did You Just Punch Out Cthulhu?: Issei's fight against Riser. He sacrifices his left arm in order to obtain some powers from his Sacred Gear. But more importantly, since its no longer technically his arm, he is able to hold the cross and utilize holy water against the otherwise undefeatable Riser without the usual repercussion of a devil holding holy items and taking damage.
Dirty Coward: After repeatedly grinding the fact that she played with Issei's heart and how his cherished first date with her was a "boring waste of time" into his face, Yuuma STILL reverts to her adorably innocent human form to beg for her life as Issei is about to strike the killing blow. She even sinks so low as to show him the armband he bought her, proclaiming how precious it is to her. Fortunately for Yuuma, Issei, even now, still fondly holds onto those warm memories as cherished moments of love and happiness, and could not bring himself to kill her. Unfortunately for Yuuma, he leaves her to Rias's discretion - whom was already going to kill Raynare, is visibly furious for the Fallen Angel toying with Issei's heartright in front of her.
Dirty Mind-Reading: Issei's Bilingual fails on Sairaorg's bishop because she's willing to strip for Issei and her breasts just say which clothing she's taking off.
Disney Death: The climax of episode 10 has Koneko getting blown up by Riser's Queen during a Rating Game and in episode 11 she fades away in a shower of sparkles. Rias explains soon after that she's just been sent to a holding area until the game ends.
Distracted by the Sexy: In episode 2, Rias attempts a demonstration of Issei's powers, and tells him to raise his left hand and concentrate. Unfortunately, she's sitting right in front of him, and higher up, so he's able to see up her skirt, and can't concentrate properly. He even points it out in his thoughts.
Does This Remind You of Anything?: Issei's Boosted Gear has the ability to double the power of the user every ten seconds at the cost of putting strain on the user. Oh the effects can also be stacked. It may remind some people of the Kaio-ken which boosts the users power, speed, defense, ki, etc. The only change produced by the basic Kaio-ken to be quantified in the series is that it doubles the user's power level. The Kaio-ken is also quite taxing on the user's body.
Downer Ending: This is how the past Boosted Gear users lives ended according to a lot of people, foremost being Ddraig. Issei has a close brush with this trope in volume 11 but revives with some help from Ddraig, Great Red, and Ophis.
Dude, Where's My Respect?: Averted with Issei. At the start he was treated as a joke by even low-tier Fallen Angels but once he started getting stronger opponents took him more and more seriously.
Early-Bird Cameo: Sona Sitri makes a brief, speaking appearance in the first episode of the anime. In the light novels she was not introduced until volume 3.
Xenovia has no issues siding with the devils in Rias' group in order to take out the Fallen Angels who have stolen some holy swords. The latter are helping partly because they're fighting a common enemy, but also because of Kiba's obsession with destroying holy swords, due to his tragic past where he was forced to take part in experiments to be able to wield them, only to then watch the other kids get killed when they were no longer useful in the experiment. As a result, the others decide they want to help him, since the end result was still getting rid of the holy swords.
Played for Laughs during Issei's first fight with Irina. He attempts to use his "Dress Breaker" move on her, but Koneko warns the girl what said ability is used for. Consequently, Irina dodges his attempts to touch her. When he complains about Koneko helping their enemy, she simply states that he is an enemy to all women.
Issei's boostgear, Ddraig, tells him about the three way war between heaven, hell, and the fallen angels during episode 8 in season 2. He mentions that for the most part, the dragons stayed out of the conflict, but two of them, himself and Albion, joined the fray. They raised such a ruckus that all three sides stopped fighting temporarily to stop the two dragons. In the end, the two dragons were chopped up, and their souls sealed in the boostgear that their respective humans have. And because of the nature of their being, they're always destined to fight each other should they meet.
Engagement Challenge: Ok so we knew Rias is engaged to the Phenex household, so Issei when comes to rescue her it becomes this to the people watching it unfold.
Everyone Can See It: It is so painfully obvious Rias likes Issei that her father acknowledges him as his future son-in-law... Same thing applies for Akeno later on, and any savvy reader notices Asia's liking of Issei from the first chapters after she's introduced.
Evil Counterpart: Vaili Lucifer and Albion are evil counterparts to Issei and Ddraig.
Fiery Red Head: Rias in a nutshell, although her power is actually destruction.
Foreign Fanservice: Slightly over a minute into the series the presence of overseas students is stated to be one of the great things about the school. When Rias is introduced, it's mentioned that she is rumoured to be Scandinavian and after the Bedmate Reveal in episode 2, Issei's mother specifically states her son's in bed with a foreign girl.
Foreshadowing: In the anime, at least. Blink and you'll miss it, but after getting Boosted Gear to work the first time, Issei deflects a bolt of Holy Lightning with it. Guess what plays a crucial role in beating Raiser?
Freeze-Frame Bonus: you can see Issei's penis in the beginning of episode 2 when his mother closes the door. Funnily enough, this gets removed in the Blu-ray version.
Friend or Idol Decision: During a break from their sparring, Azazel asks Kiba between Issei and Rias, who would he save. Kiba then flat out tells him that he'll save Rias because without her, everything is lost.
God Is Dead: Michael's the one running the place in Heaven and not God, that's why Asia can heal devils, and Kiba can dual wield a holy sword and a demon sword. The reason he died is because he pulled off a Dying Moment of Awesome by sealing a being on par with Great Red and Ophis.
Green-Eyed Monster: Issei when he's first seen by his two guy friends with Yuuma, and later with Rias. The girls also have this look when Yuto arrives to pick him up for Rias.
Guilty Pleasure: In-universe example, Issei has gone...somewhat far with some of the girls, to the point it's just short of sex.
Handshake Substitute: Issei and Kiba do the fistbump variation just before they go to their separate positions in their first Rating Game.
Hard Work Hardly Works: Subverted. Issei is mentioned constantly to be talentless and no good at anything at all. He goes through Training from Hell constantly to improve himself and in the end it worked. He turned out to be the strongest out of the Occult Club which consisted of some of the most talented individuals and some of them even had special lineages such as the the sister of the current Satan and the daughter of a leader in the Fallen Angel faction. He even eventually muched up to Vali who had the lineage of the original Satan to back himself up. The author himself mentioned that this is a series where hard work pays off and it shows. Azazel even thinks of Issei as a sponge who can absorb anything. Same thing with Sairaorg who also subverts this trope because any devil who fights off against him and loses, they don't have what it takes to bounce back since their powers don't work on someone who's just using his body as a weapon.
Harem Seeker: Issei's dream upon entering high school. Didn't quite work out, what with not being able to get a girlfriend let alone the many required for a harem. Rias promises he can get one if he does a good job as a demon. Of course, the series itself is a harem romance.
Harmless Electrocution: Issei. Whenever he gets zapped by Rassei, Asia's pet, he gets the comically electrocuted treatment, he's left with no lasting damage and is usually fine in the next scene.
Hearing Voices: Special Sacred Gears usually have something sealed within them Issei's has a red Welsh Dragon named Ddraig.
Heroes Act Villains Hinder: After creating The Alliance between the angels, fallen angels, and demons, Khaos Brigade started on terrorizing them because the three factions hate peace and/or are threatened by said peace by the three factions.
Instant Armor: Issei's Sacred Gear starts out as an Instant Gauntlet, but as it grows more powerful, it gradually expands to cover most of his arm. Then, after he sacrifices his arm to Ddraig for a short-term power-boost, his left arm BECOMES the gauntlet, and he has to use magic to keep it NORMAL. Later on, he becomes able to summon a fully-covering suit of magical armor to go with it. And of course, Vali - the White Dragon Emperor - can use HIS version of this power pretty much from the start, and does so with abandon.
Instant Awesome, Just Add Dragons: There are the three main factions: Devils, Angels, Fallen Angels, and then there are the dragons who decided not to align with any of the three and are strong enough to enforce that fact.
Knight Templar: Quite a few with the most notable being the Old Satan Faction and the Hero Faction, both absolutely convinced they're in the right and willing to do anything to get what they want.
Lap Pillow: He gets it from 3 people, Rias in Volume 2 to unseal his powers and early on in Volume 3 from Asia. Akeno joins in on volume 4.
Laser-Guided Amnesia: Rias tells Issei in episode 2 that fallen angels and demons can selectively erase themselves from human memories, such as Yuuma with Issei's two guy friends, and later Rias with Issei's parents after his mom catches them in his room naked.
Light Is Not Good: Fallen angels can still use the power of light, and they're in hell fighting with the devils.
Loads and Loads of Characters: At the start, there was only the Occult Research Club, then they added fallen angels, devils, God and his angels, dragons, exorcists, fallen exorcists, Valhalla, pretty any mythology you can think of, it's here.
Loophole Abuse: In the rating game against Riser, Rias' team does fairly well against his despite having fewer pieces/characters. Then when Issei reaches Riser, he refuses to stay down despite receiving a Curb-Stomp Battle from the latter and barely having the energy to stand. Riser then mentions that he wants to kill Issei, and that if he should happen to die during a rating game, it would be seen as an accident, rather than murder. Rias is also aware of this, and surrenders herself in order to save Issei.
Which becomes a Title Drop when you find out that Great Red is the current "D×D" known as "Dragon of Dragons". And then comes full circle when Issei becomes a "D×D" who's still in high school because Great Red used his powers with Ophis to create Issei's body.
After discussing serious issues in volume 7, Azazel asks where Odin wants to go. He immediately declares that he wants to go to a breast club much to the consternation of the group.
Volume 12 starts out depressing after what happened in the previous volume. And then, it's now at Issei's perspective of the story where the first few things that he says is that he can't even make out with Rias anymore with his current spirit form.
Naked Apron: Issei sees Asia wearing one during season 2. When he protests that his parents would be mad if they saw her like that, his mom pops out from the kitchen, stating she was the one that came up with the idea. Rias then decides to do the same as well.
No Pronunciation Guide: So, how does one pronounce the "Dx D" portion of the title? Dee-Ecks-Dee? D versus D? D against D? D and D? D cross D? It's rather ambiguous to say the least. However, info from the official website suggests that the 'x' is silent, giving us "Dee-Dee" as the correct pronunciation.
Of course, this is rectified when they reveal that D x D means "Dragon of Dragons". Still no idea where the "of" came from, but that does kind of partially solve the issue.
Our Angels Are Different/Our Demons Are Different: Demons and fallen angels are two separate classes of beings: demons are the original inhabitants of hell, whereas fallen angels are interlopers who settled there after getting kicked out of heaven. The two groups have been at war ever since.
Peace Conference: Happens in the fourth volume. It was successful, however there is a certain faction who doesn't want in.
Panty Shot: The ratio of panty shots to pages in the manga is virtually 1:1.
Peeping Tom: The first scene in the novels involves Issei and his friends Matsuda and Motohama peeking at the girls locker room.
Physical God: Gods in this series are extremely strong. Loki, for example, could hold off the two strongest members of the Fallen Angel group plus the entire Occult Club plus Saji in his dragon from with ease. Also Son Wukong has been shown to utterly crush the Hero Faction which are each individually at a High Ultimate-Tier Devil level. The two strongest beings, Ophis and Great Red, are represented by Infinite and Dreams which say volumes of how strong they are.
Vali invokes this to Issei that the latter is ranked somewhere in the 4 digits and that Sirzechs won't enter the top 10.
According to Word of God, this is who Vali meant when he referred to the top 10. Disregarding Great Red, we have (in no particular order): Ophis (before her Nerf), Shiva, Vishnu, Brahma, Śakra, Thor, Typhon (or Fenrir and this is before its Nerf), Hades, Aten, and Lugh.
The devils also have a strength tier with ultimate being the highest level and low-level devils being the lowest. In a subversion, however, the entire Occult Club with the exception of Rias are all low-level devils and they are all considered with the exception of Asia and Gasper until his Curb-Stomp Battle with Georg to be high-level devils if not stronger. Ironically Rias herself ends up as one of the weaker members with most of the rest of the Occult Club surpassing her.
Note that this is not a good thing. The first time it happens is when he thinks Asia has been killed by Shalba. He loses his shit and literally eats the guy alive. Issei on The Power of Love is absolutely terrifying.
Pretty Freeloaders: Asia is the first one who stays at Issei's home, then later on it's Rias, Akeno, Koneko, Xenovia, Irina, and Rossweisse who stay with him while Kiba and Gasper rent a house near them. Kuroka and Le Fay also get in on the action in the most recent novel.
Pun: Upon seeing Serafall Leviathan, one of the Four Satans, Issei dubs her a "Maou Shoujo". note Demon King Girl, as opposed to Mahou Shoujo, Magical Girl.
Issei's Boosted Gear in general is very much like Kazuma the Shell Bullet from S Cry Ed.
When Gasper is first introduced, he takes to hiding in a cardboard box, making a Metal Gear Solid reference by referring to himself as a snake and Issei as Big Boss
Sick Episode: One of the short-stories in volume 13 has Issei becoming sick after catching a flu for devils and dragons.
Someday This Will Come in Handy: Back in volume 4, Sirzechs asks Issei what would happen if Issei used Gift on Rias' breasts then tells the latter not to worry about it, which obviously makes Issei think of a lot of crazy outcomes on what will happen. It mostly gets forgotten, until Volume 11 where the spirits of the past users of Boosted Gear bring it up again. It replenishes Issei's aura at the cost of Rias' breasts shrinking.
Stripperific: The outfits the girls wear in the ending for season 1.
The Legend of Oppai Dragon and his Lively Companions (Vol. 14-present)
Short Story collections (Vols. 8, 13, and 15)
Story Breaker Power: Ophis displays zero interest in fighting, because if she ever got serious, she would destroy every opponent easily and thus finds fighting with anybody except Great Red pointless. Even when weakened to around 25-50% of her true power, she's still double the strength of the two Heavenly Dragons.
And even she pales compared to what Great Red can do. He combines with Issei, made him Kaiju-sized, and told Issei to use his Dangerous Forbidden Technique (Longinus Smasher), and with some assistance by Grayfia and her group just to launch the enemy in the air, obliterates the giant monster who has an instant regeneration. All Issei could say after that was "Amazing".
There's also Son Wukong, who easily blocked the True Longinus with one finger and forced the entire Hero Faction to retreat.
Various from Sacred Gear to Sacred Gear. Kiba has the the ability to create swords with any special element he wants. Vali could Divide someone's power by two every ten seconds and Issei could double his own power by two every ten seconds. Gasper could stop time. Then there's Cao Cao who has the True Longinus that has 7 abilities which are all utterly broken such as the ability to destroy all weapons and a Attack Reflector.
Also besides Sacred Gears there are people that are born into a special lineage which gives them special power exclusive to their family. Rias's family has the Power of Destruction, for example. Vali once again wins this lottery because he is the descendant of Lucifer thus he has great magic power that further boasts the power of his Sacred Gear by allowing him to feed his magic power for Juggernaut Drive which allows him to be the only person that could use this ability without drawback.
Surrounded by Idiots: Angels, Fallen Angels, and Devils all suffer from this early in the series. The first few story arcs present the Fallen Angels as the default villains, but the leaders of all three factions are cool guys entirely willing to get along, while most of the trouble gets stirred up by their overzealous or rebellious subordinates. Largely phased out as they become The Alliance in favor of more external threats.
Take That: Zatuji, the "Familiar Master" in Episode 7. He is a middle-aged man who dresses and talks like Ash Ketchum/Satoshi is a not-too-kind jab at the Pokémon fandom, particularly adults who refuse to "let go." Ironically, the author admits that he's a fan of Pokémon in the volume 8 afterword, and his artist told his editor to make that story.
Talking Is a Free Action: When Issei first uses Balance Breaker, Ddraig warns him that it's only good for 10 seconds because Issei can't handle the stress of Boosted Gear. Yet, when he's fighting and talking against Raiser, their conversation lasts for a few minutes while Ddraig is counting the number of seconds till Balance Breaker is up.
The Anime fixes this, mostly by having Ddraig say he'll "count to ten" without actually specifying seconds. His count during the action is slower than seconds, but consistent, and the talk between Issei and Riser is much snappier.
Teeth-Clenched Teamwork: The Khaos Brigade, in general, is this. Ophis may be the overall leader, however the three main groups have different agendas. Vali's group is the closest one who wants to fulfill Ophis' wish to kick out Great Red from the dimension gap only because Vali wants to fight the strongest being. The Old Satan Faction only uses Ophis to regain Hell and wage another Forever War to prove that the devils are the strongest. The Hero Faction just wants to wipe out all the mythologies and prove that they're heroes.
Training from Hell: Rias' training of Issei is nothing but this. Later on, he gets subjected to this by Tannin who trains him literally in hell.
A Truce While We Gawk: In volume 7 while an epic battle is going on, Issei somehow summons a breast god (yes, there is apparently one in the universe). When he announces this, everyone on both sides stop fighting and start staring at him as if he's done something stupidly crazy again...
Two-Teacher School: The only teachers who are even active in this school are Azazel and Rossweisse.
Ultimate Showdown of Ultimate Destiny: All the different mythologies are in this series, and the only thing that's keeping them from waging war with each other is that The Alliance (devils, fallen angels, and angels) wants to make peace with other mythologies. According to Sakra Indra, the other mythologies may be cooperating on the surface, but deep down they want to destroy the other mythologies.
Unprovoked Pervert Payback: Despite numerous amounts of Fanservice, this show averts it. Hell, even Issei expected that Rias was going to hit him when she caught Koneko and him naked. Turns out, Rias just examined Koneko and stated that she needed a doctor.
Unwitting Pawn: The Occult Research Club to Vali in Volume 7 seeing as the latter wanted Fenrir on his side, thereby fighting alongside them, and the Hero Faction in general to Hades.
Valkyries: They exist in the universe, as Odin is a character within the story Later on, one of those Valkyries becomes Rias' new Rook, Rossweisse.
What Does She See in Him?: It has been stated throughout the story from people wondering why Rias and Asia are close to Issei later on Koneko, a church assassin named Xenovia, another church assassin-turned-angel named Irina, Akeno, and Ravel Phenex. If only they knew the crap he went through for the girls.
Whole Volume Flashback: While interspersed with current events, the entire Volume Fifteen will talk about the different pasts of other characters and other events that was never mentioned in the light novels.
Will They or Won't They?: Rias does love Issei, but it takes 10 light novel volumes before he finally says it back to her. Might have something about his dying on his first date issues.
Winged Humanoid: Everyone that's on one of the three factions. The Angels and their Fallen former comrades have the feathery kind (normal angels have white wings while those of Fallen Angels are black), Devil wings are more bat-like or perhaps Draconic.
Would Hit a Girl: Pretty much almost every male in this series has no problems fighting against women at all. Finally, we don't get a loser protagonist who sits there and lets the resident Tsundere whoop his ass at the slightest infraction.
That said, Issei is still punished quite often for his perversions, usually by Koneko.
Xanatos Speed Chess: Well, the Rating Game is a team battle that involves adjusting the strategies in response to the opponents actions.
You Have Outlived Your Usefulness: Happens to a bunch of kids that were part of an illegal, forced experiment to wield holy swords. Turns out none of them were able to do it, and when the project was discovered later, it was shut down, and the kids were exterminated instead of freed. Kiba was one of the children, and the others sacrificed themselves in order to give him a chance to escape. He later vows Revenge for them, and Rias takes him in so that he could serve her instead of dying in the forest.