* ActingForTwo:
** Ile and Nell are both voiced by Chinatsu Akasaki in Japanese and by Lara Woodhull in English.
** In the Japanese version, in addition to voicing Isabella in the anime's first season, Harumi Sakurai voices Katerea Leviathan in the ''New''.
** Akeno Himejima and her mother Shuri are both voiced by Creator/ShizukaIto in Japanese.
** In the English dub of ''[=BorN=]'', Grayfia and Ophis are both played by Megan Shipman.
* BannedInChina: The anime adaptation of ''DXD'' was refused classification in New Zealand, on the count that it "promotes child pornography". On the other hand, the series is available in Australia. The anime has been banned in China as well for excessive sexual content and graphic violence.
* CastingGag:
** It's not the first time Creator/AyanaTaketatsu (Koneko's [=VA=]) has voiced a cat [[Manga/CatGod before]].
** The same goes for Koneko's English actress Creator/JadSaxton, as she previously voiced a cat, [[Manga/FairyTail except she came from a different universe]].
* ChannelHop: An animation studio variation. {{Creator/TNK}} handled the animation production for the first three seasons, with Tetsuya Yanagisawa as director. For ''Hero'', the series was produced by Passione with a completely new crew and was now directed by Yoshifumi Sueda.
* CreatorBacklash: After ''[=BorN=]'' was broadcast, Tetsuya Yanagisawa and Ichiei Ishibumi both admitted it wasn't the season they were hoping for because the former changed elements of the light novel's fifth through seventh volumes for the season against Ishibumi and Yoshioka's objections. Then, Ishibumi wrote the ''EX'' spin-off to turn it into an AlternateContinuity. It would turn out to be the last season with which Yanagisawa and TNK were associated.
* DeletedScene: There are extra scenes in ''New'' that didn't make the broadcast run due to time limitations, but were restored for the Blu-ray/DVD releases.
* DirectedByCastMember: Three cast members directed the English dub of the anime. The first was by Creator/ColleenClinkenbeard, who voiced Shiro and Xuelan; the second by Creator/ChristopherSabat, who voiced Ddraig; and the third by Cris George, Creuserey Asmodeus's English VA.
* ExecutiveMeddling: At one point, Ishibumi intended to have Issei suck Rias's breasts, but Fujimi Shobo nixed that idea.
* FlashbackWithTheOtherDarrin: For the dub of ''[=BorN=]'', all of Scott Freeman's dialogue as Issei in the flashbacks were redubbed by Josh Grelle due to erratic behavior on Freeman's part.
* FanNickname:
** Hypnobutt - Koneko [[MaleGaze swaying her butt on the screen in the ending]]
** Weapon [[{{Netorare}} NTR]] - [[spoiler: for Issei and Kiba ''hijacking'' both True Longinus and ''all'' of Siegfried's swords respectively.]]
** GAR-sper - In some circles, Gasper after his awesome moment in Volume 10.
** [[Manga/{{Bleach}} Kenpachi dragon]] - Grendel is called this in the {{Imageboard}}s thanks to his BloodKnight attitude while fighting Issei.
** Dragon swag - What fans refer to when Issei attracts someone's attention.
** Dickora - for Diodora, which further cements his HateSink status.
* IKnewIt:
** Some people got it correct when [[spoiler:they thought that Great Red was going to help out both Issei and Ophis. ''No one'', however, thought that Great Red has a {{Delinquent}} personality.]]
** Quite a few people guessed correctly that Passione [[http://www.animenewsnetwork.com/news/2017-10-21/high-school-dxd-hero-anime-promo-video-streamed/.123018 will animate the fourth season]].
* NamesTheSame: Sister Asia Argento shares the same name with the famous Italian actress Creator/AsiaArgento.
* NetworkToTheRescue: After the backlash against ''[=BorN=]'', Passione picked up the series to animated the fourth season, ''Hero'', and included the same voice cast to boot.
* NoExportForYou:
** The licensed games for the 3DS and PS Vita have only been exclusive to Japan.
** The anime won't be released in China or New Zealand anytime soon due to its violence and sexual content.
* OldShame: Tetsuya Yanagisawa and Ichiei Ishibumi have expressed regret on how ''[=BorN=]'' turned out.
* TheOtherDarrin: For the dub of the final Tetsuya Yanagisawa/Takao Yoshioka/Junji Goto/TNK season:
** Creator/JoshGrelle replaces Scott Freeman as Issei due to the latter's arrest for child pornography.
** Kelly Angel replaces Teri Rogers as Akeno. The dub acknowledges this in a very ''Series/{{Roseanne}}'' like way in the second episode.
--> '''Venelana''': You sound so different, Akeno!
** Megan Shipman replaces Krishna Smitha as Grayfia due to the latter being involved in mostly union-only projects after moving to Los Angeles.
* PlayingAgainstType:
** In the dub, the cultured and flirty Devil Rias Gremory is voiced by the [[{{Lust}} lustful]] and [[SirSwearsALot foul-mouthed]] FallenAngel [[Anime/PantyAndStockingWithGarterbelt Panty Anarchy]].
** Again with the dub, the perverted nice guy Issei Hyoudou is voiced by [[WebComic/AxisPowersHetalia United Kingdom]], the [[MeanBrit fake]] [[QuintessentialBritishGentleman British gentleman]]. At least, for the first two seasons.
*** For the third season, Issei gets ''two'' Playing Against Types: [[Creator/JoshGrelle he is voiced by]] the fearful UnluckyEverydude [[Manga/FutureDiary Yukiteru Amano]], as well as [[LightNovel/InfiniteStratos Ichika Orimura]], the one guy in an all-girls academy who has an UnwantedHarem [[CluelessChickMagnet and is all the oblivious about it]].
* RelationshipVoiceActor:
** Although it was a short-lived one, Creator/ShizukaIto and Creator/HitomiNabatame reunite here as Akeno and Raynare.
** Creator/ScottFreeman and Creator/JamieMarchi played another OfficialCouple in ''LightNovel/BakaAndTestSummonTheBeasts'' (Yuuji and Shouko).
** ''New'' reunites [[Creator/AyaneSakura Akane Isshiki]], [[Creator/MaayaUchida Rei Kuroki]] and [[Creator/HarukaYamazaki Mizuha Amagi]] from [[Anime/VividredOperation Vividred Operation]] but ironically their characters will never get to interact with each other in the anime.
** Also in ''New'', [[Creator/YokoHikasa Emilia Justine]] [[LightNovel/TheDevilIsAPartTimer and]] [[Creator/RyotaOhsaka Satan Jacob]] are reunited but at least this time, Emilia isn't out for Sadao's blood. But if Issei is hurt...
*** [[Creator/AzumiAsakura Emerlda]] was already there. [[Creator/HirokiYasumoto Albert]] pops up to but he's evil now.
*** Remember that [[BadassBystander awesome convenience store worker]] that threw paint balls at Emilia's attacker? He's [[Creator/YuuichiIguchi Saji]] over here.
** [[Creator/HirokiYasumoto Kokabiel]]: [[Creator/YuukiKaji Issei]], [[LukeIAmYourFather I am your father.]] [[Anime/AquarionEvol 12,000 years ago...]] And he's also [[VideoGame/AsurasWrath Asura]]. Though he got demoted from demi-god to fallen angel, no ''wonder'' the Gremory team couldn't even scratch him.
** [[Creator/YuukiKaji Issei]] and [[Creator/YuuichiNakamura Sairaorg]] have ''a lot'' in their list. [[Manga/DontenNiWarau Fortunately,]] [[VideoGame/FinalFantasyXIII they're]] [[Anime/GuiltyCrown allies]] [[Anime/AquarionEVOL this]] [[Anime/{{Durarara}} time]] [[Anime/FairyTail instead]] [[Anime/NobunagaTheFool of]] [[Anime/NobunagaConcerto enemies.]]
** Quite a lot of the voice actors present were also involved in VideoGame/StreetFighterV - [[Creator/YokoHikasa Rias]] was Laura, Taketora (Dohnaseek) was Akuma, [[Creator/JunichiSuwabe Lucifer]] was Vega, [[Creator/KentaMiyake Mil-tan]] was Zangief, [[Creator/HirokiYasumoto Kokabiel]] was Guile, Ryota Takeuchi (Albion) was Abigail.
** For the dub, [[Anime/PantyAndStockingWithGarterbelt the Anarchy Sisters]] reunite in the third season as [[Creator/JamieMarchi daughter (Rias/Panty)]] and [[Creator/MonicaRial mother (Venelana/Stocking)]].
* RoleEndingMisdemeanor: Creator/ScottFreeman originally voiced Issei Hyoudou in the dub of the first two seasons. When he was arrested and convicted for possession of child pornography in 2015, Creator/JoshGrelle replaced him for the third season.
* ScrewedByTheNetwork: When Tetsuya Yanagisawa went over Ichiei Ishibumi and Takao Yoshioka's heads in adapting volumes 5 to 7 for the third season of the anime.
* SleeperHit: Of the {{Winter 2012 Anime}} season. No one expected that the series would even sell 10,000 DVD [=/=] Blu-ray copies in the first week! [[AndYouThoughtItWouldFail Hoo, boy, were they wrong]].
* WhatCouldHaveBeen:
** Supposedly, one of Issei's power-ups was to ''suck Rias' breasts''. Unfortunately, that was already too much for Fujimi Shobo, so Ishibumi resorted to something else.
** Ishibumi has said that he almost wanted to make Kiba as the main character instead of Issei. However, that didn't come into fruition.
** Ishibumi considered resurrecting Freed with the Holy Grail, and bonding his soul to an evil dragon. He ended up deciding to let him stay dead.
** Ishibumi reportedly considered making ''[=BorN=]'' a bit longer than usual given the extent of the novels that it would cover. However, Tetsuya Yanagisawa trimmed down the novels to fit a twelve-episode season as the previous two have been and added the subplot of Loki corrupting Rias and Issei, over Ishibumi and Takao Yoshioka's objections. In response, Ishibumi wrote ''EX'' to make the second half of the series an AlternateContinuity.
* TheWikiRule: [[http://highschooldxd.wikia.com/wiki/Main_Page Sure thing, dawg!]] '''WARNING:''' Gets a little NSFW in some places.
* WordOfGod: Series creator Ichiei Ishibumi, who contributes to his Twitter feed and light novel afterwords to explain some important aspects of the series like character histories and has answers to questions regarding character names.