[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/chaoshead_anime.jpg]]
[[caption-width-right:350:Who's eyes are those eyes?]]

->''"If you are God and the delusion becomes reality.\\
About what kind of the noids you get?\\
Is it the sensual world? The despotic society?\\
The destructive sanctions?\\
Or..."''

''Chaos;Head'' is an anime based off the VisualNovel that is the first entry in the VisualNovel/ScienceAdventureSeries starring Takumi Nishijou, an OrdinaryHighSchoolStudent and raging {{otaku}} who lives in the Tokyo ward of Shibuya.

Takumi lives in a steel shipping container on the roof of a building, converted into a small apartment. He spends most of his time at home, either playing the {{fictional|VideoGame}} {{MMORPG}} ''Empire Sweeper Online'' (in which he is Neidhardt/Knight-heart, the most famous and powerful player ever) or watching anime. He has over one hundred "waifus" (figurines), his favorite being the character Seira from the [[ShowWithinAShow fictional anime]] ''Blood Tune''; he frequently affirms his love of 2-D women and his hatred of 3-D women. He is a borderline {{hikikomori}}, having crafted a "minimum attendance shift chart" to ensure that he can attend school as little as possible while still graduating.

When the story begins, he is only known to have even semi-regular interactions with a few people: his [[AnnoyingYoungerSibling bratty younger sister Nanami]], his ESO [[BandOfBrothers guild partner Grim]] (whom he speaks to online), the school's [[HandsomeLech resident playboy Misumi]], and Seira, whom he has become deluded into thinking exists, to the point that he can hear her talking and interact with her as a kind of muse. Beyond these, he seems to be quite afraid of interacting with people, exhibiting classic signs of social phobia (such as extreme discomfort with making eye contact).

This routine life is shattered when, upon coming home one day, he hears the [[HellIsThatNoise sound of something being pounded into concrete]]. Looking over, he sees a [[GirlWithPsychoWeapon pink-haired 'demon girl']], [[CruelAndUnusualDeath pinning a body to an alley wall with cross-shaped stakes]]. The girl turns, smiles, and inexplicably calls him by name, at which point he runs. This scene is the third in a series of bizarre, gruesome murders called the "New Generation" murders. Takumi initially wants nothing to do with this, but a mysterious user known as 'Shogun/The General' begins stalking Takumi, and seems intent on dragging him into the whole mess. Takumi then realizes that this mysterious man is working with the demon girl. Meanwhile, the [[MegaCorp Noah OrganiZation Of Medical Instruments, or the NOZOMI Group]], puppeteers the New Gen incidents for their hidden, sinister purposes. When the bodies continue to pile up, a whole bunch of weird super-powered girls show up and [[HaremGenre get closer to Takumi]], a conspiracy between NOZOMI and several powerful organizations surfaces, and, in the center of it all, [[BigBad Shogun/The General]] and the [[TheDragon Demon Girl]] make their move, Takumi finds himself forced out of his solitary lifestyle, and into a mystery encapsulating all of Shibuya.

The [[AnimeOfTheGame anime]] was made by Creator/{{Madhouse}} for the fall 2008 season.

A Main/{{Sequel}}, ''VisualNovel/ChaosChild'', was released for the Platform/XboxOne in 2014, with different cast of characters in the same setting of Shibuya. The [[http://www.crunchyroll.com/chaoschild anime adaptation]] started airing in January 2017. An official English version was released on Platform/{{Steam}} in January 2019.

!!This series provides examples of:
* ActuallyADoombot: In Episode 8 of the anime, Takumi, Sena, and Kozue confront and defeat [[spoiler:Genichi, and destroy [[DoomsdayDevice Noah II]]]]... only for the real [[spoiler:Genichi]] to reveal that the [[spoiler:Genichi]] they fought was a delusion he implanted in their minds, and [[spoiler:the Noah II they destroyed was a prototype]].
* AdaptationDistillation: It takes around 25 to 30 hours to finish the game (or at least the common route which is the canon events of the story). The anime adaptation, on the other hand, is little short of six hours long. It hardly takes a genius to figure out how much of the story was left out in the adaptation.
* AdaptationExpansion: The anime introduces Ayase's cocytus-delusion, which functions as a freezing attack. Additionally, the events of Episode 8 (in which Takumi, Sena, and Kozue launch an attack on [[MegaCorp Nozomi]] headquarters) are anime-only.
* TheAnimeOfTheGame: The original PC game was released on August 26, 2008. The TwelveEpisodeAnime ran from October 9 to December 25, 2008.
* CuteClumsyGirl: Kozue. Also Yua, in this adaptation.
* BittersweetEnding: Following Ending A of the original game, it is slightly more sweet that bitter. [[spoiler: Although the real Takumi is dead, and Sena's father saved Sena at the cost of his own life, the clone Takumi finally realizes and confesses his love for Rimi, all of the other gigalomaniac girls managed to survive, Kozue even regained her normal, non-telepathic voice, and the world was saved.]]
* {{Expospeak}}: Halfway through the anime, the characters seem to replace their Unreliable Narrator tendencies with massive amounts of equally unreliable technobabble, signifying that everyone in the series has psychological issues.
* LighterAndSofter: The anime adaptation is tamer in both violence and horror. Also, some of the murders were removed due to this being a CompressedAdaptation.
** Nortose's cruel MindRape attack on Takumi was replaced by a peaceful delusion based on the bad ending (Crying Sky).
* SpoilerOpening: The gradual reveal of the different Gigalomaniacs throughout the story isn't quite as exciting after you see all but two of them with their Di-Swords in the opening.
** The Reveal of [[spoiler: Norose as the Big Bad, rather than Shogun]], is also somewhat spoiled in the anime OP by the shot of him grinning maniacally.
** There's also the shot of [[spoiler: Hazuki and Suwa together, which hints towards the fact that they are related somehow as the New Gen killers.]]
* TwelveEpisodeAnime: The anime have twelve episodes.