* ActingForTwo: Kokoro shares a VA with Youko, Sekai's mother, in all adaptations, though they don't interact much, if at all unless you count the ''Magical Heart Kokoro-chan'' OVA.
* CreatorsFavorite: The JAST interview has Mathers Numakichi claim that he loves all his characters equally, but Setsuna is at the top of the list.
* CutSong: The Series Complete Box includes five tracks not found on any of the previous soundtrack album releases or in the games themselves, including a song titled "Liar in the Mirror" sung by Kotonoha & Sekai’s [[TheOtherMarty original voice actresses]]. One of them, "Knife or Saw?", was heard in the pilot film.
* TheDanza: Minami Obuchi is voiced by Minami Kuribayashi.
* DevelopmentHell: ''VisualNovel/CrossDays'' was delayed no less than SIX times, from its original release date of February 2009 to March 19th, 2010.
* DistancedFromCurrentEvents: The "Nice Boat" incident. To summarize: [[spoiler:The last episode of the TV series features Sekai brutally stabbing Makoto to death, Kotonoha cutting off Makoto's head, Kotonoha slitting Sekai's throat, cutting her stomach open to confirm whether she was pregnant, then sailing away with Makoto's severed head.]] The day before the episode was supposed to air, a 16-year-old Japanese girl murdered her father with an axe, so the episode had to be pushed back a week, and its slot replaced with a thirty-minute slideshow, which included a shot of a boat.
* FanTranslation: A partial translation patch was released in August 2010 by Sekai Project and endorsed by the game's maker, 0verflow. Later, when the game was licensed, [[PromotedFanboy the fan translators became the official localization team.]]
* InspirationForTheWork: [[WordOfGod In an interview]], Mathers Numakichi stated that his intention with the series was to make a game that was entirely animated, and told a bizarre story like ''Film/{{Fargo}}'' did.
* KeepCirculatingTheTapes: The Platform/PlayStation2 port is the only version of the game that was created specifically to be for a younger audience (15+) instead of an adult game. As such the game has new scenes made for the routes that used R content in the original game. It also contains special epilogues for the (then three) "Bad endings" of the original game as well as many brand new bad endings. All this new content wasn’t added to the HQ version that came out later so it remains exclusive to the [=PS2=] version to this day. Sadly the port was Japan exclusive and is no longer in production so copies can only be obtained from second hand stores like [=eBay=].
* LateExportForYou:
** The first officially licensed English version of the visual novel didn’t come out until [[https://www.animenewsnetwork.com/news/2011-03-01/jast-usa-adds-school-days-hq-visual-novel-software 2012.]] 7 years after the original’s release and 5 years after the anime ended.
** For several years, it was assumed there'd be no Western localization of the anime due to the [[DownerEnding infamous]] [[{{Gorn}} ending]] and [[DistancedFromCurrentEvents the circumstances]] [[ExecutiveMeddling regarding it]]. Then after a long wait, the anime was made available for streaming [[https://www.crunchyroll.com/school-days on Crunchyroll]] in the U.S, and was eventually picked up for a proper release by Creator/DiscotekMedia.
* MeaningfulReleaseDate: Creator/ShihoKawaragi chose to debut her Sekai [=VTuber=] on July 3, 2022, exactly fifteen years to the day after the first episode of the anime aired.
* NoExportForYou:
** The manga, unlike the anime, will stay in Japan. According to a notice from a major manga publisher in Argentina, [[http://www.editorialivrea.com/secretos/preguntas/comment-page-28/#comment-13252 Kadokawa (who published the manga in Japan) won't authorize any foreign releases of the manga outside Japan]].
* TheOtherMarty:
** In the promotional pilot, Sekai and Kotonoha have different voice actress, being played by Chiaki Ōsawa (credited as Eri Sakurada) and Akira Kasahara (credited as Mitsuki Ueno) respectively before being replaced in the main game and all subsequent media by Creator/TaeOkajima and Creator/ShihoKawaragi. The original voice actresses also sang the CutSong "Liar in the Mirror" and an ending song for ''Miss Each Other'' under the group label "unity", which was disbanded shortly afterwards.
** Otome is voiced by Mikako Satō (under the alias [[PornNames Hina Kamimura]]) in the trial demo, but was replaced[[note]]According to the Japanese Wikipedia, Sato was unavailable due to being hospitalized by a traffic accident after recording the trial audio[[/note]] by Haruka Nagami in the finished game.
* PenName: Mathers Numakichi, the creator of the ''School Days'' series and main scenario writer, is believed to be a pseudonym for Akio Ōnuma, the founder and CEO of [=0verflow=]’s parent company Stack.
* ReferencedBy: "[[MemeticMutation Nice Boat]]" and some iconic scenes from ''School Days'' get referenced by other anime:
** ''Anime/HellGirl'': In Episode 21 of season two. A guy named Makoto coldly rejects the woman pregnant with his child.
** ''Anime/AikatsuStars'': As a form of GagCensor: Episode 37 had Mahiru struggle breaking her tiles, so she "violently" starts breaking them apart piece by piece behind a scene of a boat on a lake...
** ''Anime/YukiYunaIsAHero'': One scene in the ''Jukai no Kioku'' game suddenly cuts to a scene of a boat on a lake, referencing the infamous "Nice Boat" meme from ''School Days''. One of [=YuYuYu=]'s writers, Makoto Uezu, was also a writer for the ''School Days'' anime.
** ''[[Literature/MyMentalChoicesAre My Mental Choices Are Completely Interfering with My School Romantic Comedy]]'': The OVA keeps up with the ''School Days'' references by recreating the infamous "There's nobody inside." scene near the end of the episode.
** ''[[VisualNovel/HigurashiWhenTheyCry Higurashi]] Day Break'': In the PSP game, Natsume's charge move looks a lot like what Sekai does to Makoto in the finale of the ''School Days'' anime.
** ''AudioPlay/YandereNoOnnaNoKo'': Sonoko is an {{Expy}} of Kotonoha Katsura, with a bit of an {{Irony}} that Sonoko is voiced by Creator/ShihoKawaragi, the actor of Kotonoha's fellow {{Yandere}} rival, Sekai Saionji.
** ''Manga/DailyLivesOfHighSchoolBoys'': Applies only to the Cantonese dub. In multiple places, people referred to "Makoto, scum of the earth." This is the epithet for ''School Days''’ Makoto Itou among anime watchers in Chinese-speaking regions.
** ''Manga/PopTeamEpic'': At the start of Episode 5, the "Steamboat Willie" parody is censored with [[MemeticMutation footage of]] a boat. Later on in the episode, we have a skit with Popuko doing her impression of [[WritingAroundTrademarks Mi**ey]], and we only get to see it via her shadow. The boat censorship, which was placed there to indicate "violence and adult issues" which were deemed harmful to minors, also doubles as one in and of itself if you know [[VisualNovel/SchoolDays the reference]]: the following skit, "IMO☆YOBA", which was ''not'' censored, sees Iyo Sakuragi [[spoiler:snap and attempt to stab Pipimi with a knife, only for Hojo-senpai to take the hit. Complete with {{Gorn}}]].
** ''VideoGame/HatsuneMikuProjectDiva'': The PV for ''Watashi no Jikan'' makes good on a couple of old memes, mainly Nice Boat and [[Memes/{{Bleach}} Leek Spin]].
** ''VideoGame/HonkaiImpact3rd'': The "Nice Boat!" achievement is a reference to the last anime episode.
** ''Series/KamenRiderAmazons'': The episode involving a star-crossed couple and decapitations, amusingly, happens to be named School Days.
** ''VisualNovel/MajikoiLoveMeSeriously'': In the Miyako route, the group catches a stalker named "Ito Makoto".
** ''Literature/{{Oreimo}}'': In the pilot episode of the anime, when Kirino shows Kyousuke her large stack of H-games, several real-life titles can be spotted in said stack, including (but possibly not limited to) ''School Days'', ''Summer Days'', and ''Cross Days''.
** ''Manga/TheWorldGodOnlyKnows'': In Chapter 3, p.2, Keima is playing a galge in the middle of class as usual, but if you pay attention to the text that comes out of his headphones, you'll notice he's playing ''School Days''.
** ''VideoGame/YandereSimulator'': Akademi Uniform Style 5 bears a resemblance to the uniforms from ''School Days''. Fitting, really for a game featuring a {{Yandere}}.
* RefittedForSequel: As stated under WhatCouldHaveBeen, one of the original three bad endings was going to be "Pushed Too Far" in which [[spoiler:Sekai pushes Kotonoha in front of a moving train]], but the final game replaces this with “Forever” in which [[spoiler:she is SpurnedIntoSuicide and dives headfirst from the apartment building in front of Makoto and Sekai]]. The ''School Days HQ'' remaster adds "Pushed Too Far" as a new bad ending, and the ''School Days [=L×H=]'' port for [=PS2=] includes several new bad endings, all of which are permutations of this original concept but with the final victims varying between them.
* VirtualYouTuber: Kotohona debuted as a [[https://www.youtube.com/channel/UCpUo_pV1WmPsB4qJnIzoXQQ VTuber]] on Christmas 2020. Creator/ShihoKawaragi’s own [=YouTube=] channel would later host [[https://youtu.be/OGe4NEms7DA Sekai as a VTuber]] in July 2022.
* WhatCouldHaveBeen:
** The prototype anime pilot to promote the game (included on the Series Complete Box) shows a number of differences from the finished product. The art style is noticeably different, as are some details of the bad endings. The "Forever" ending where [[spoiler:Kotonoha is SpurnedIntoSuicide]] replaces the "Pushed Too Far" ending in the final cut (though the latter was RefittedForSequel in the remakes), the “Bloody End” took place at the school rather than [[spoiler:the overpass at the train station, with bystanders attempting to hold back the killer]], and [[spoiler:Makoto’s walk on the beach as he bleeds to death [[ArsonMurderAndJaywalking goes in the opposition direction and happens in the daytime]] in “To My Child”]].
** ''Magical Heart Kokoro-chan'' has slightly different choreography for the TransformationSequence between the trailer and the OVA, though some animation is reused between them.
* WordOfGod: The ''Shiny Days'' art book includes [[https://themanwithpants.tumblr.com/post/130917785978/jast-shiny-days-interview-with-school-days-series an interview]] by JAST with series creator Mathers Numakichi, who explains certain details like ''Fargo'' being the InspirationForTheWork.
* Rather hilariously, one of the producers of the anime is also named Makoto Itou (though the name is really common in Japan), and his name can actually be seen in the opening credits.
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