[[caption-width-right:300:You only wish it were a harem show.]]

->''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?\\

''Chaos;Head'' is a VisualNovel starring Nishijou Takumi, a high school student and raging otaku.

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 [[FictionalVideoGame fictional]] {{MMORPG}} ''Empire Sweeper Online'' (in which he is Neidhardt, the most famous and powerful player to exist) or watching anime. He has over one hundred "waifus" (figures), 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 she exists and can hear her talking and interact with her as 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 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.

The game has a unique "delusion trigger" system where the player can, at certain points, opt to view one of Takumi's daydreams/delusions. The player is given a choice between a good delusion (happy, humorous, or [[{{ecchi}} H]] in nature) or a bad delusion (paranoid, violent or tragic in nature). For example, when Nanami visits and berates Takumi for not ever calling home, she takes a swig of soda without asking; the good delusion brings up the concept of an IndirectKiss, prompting Takumi to compare it to a [[{{Eroge}} hentai game]] scene (at which point it almost does turn into one), and the bad delusion involves Nanami taking a swig of coke, then gagging and coughing up blood and dying. Takumi wonders why that happened, then remembers that he poisoned the coke beforehand. Typically these delusions have no direct influence on the story itself (Takumi simply snaps out of it and the scene continues from where it left off), but seeing certain ones triggers flags that can influence which ending you see. Many of these delusions involve blatant reference to anime (or eroge) tropes.

The [[AnimeOfTheGame game was made into an anime]] by Creator/{{Madhouse}} for the fall 2008 season, with an Xbox 360 updated rerelease titled ''Chaos;Head Noah'' released in February 2009. [[http://www.youtube.com/playlist?list=EL7jKqPFu85Ss Three episodes are available on FUNimation's Youtube channel.]]

A fan translation patch for the game exists, but was taken down from the main site due to an agreement with Nitroplus, which unfortunately lead to DevelopmentHell as there's no localized version of the game yet, in fact no news after the "agreement" between the original fan translators and Nitroplus were given.

The game is the predecessor to ''VisualNovel/SteinsGate'' and ''VisualNovel/RoboticsNotes''.

A Main/{{Sequel}}, [[https://vndb.org/v14018 Chaos;Child]], was released for the XboxOne in 2014, with different cast of characters in the same setting of Shibuya.
!!''ChaosHead'' provides examples of:

* ActionGirl: Sena.
* AdaptationDistillation: It takes around 20 hours to finish the game (or at least one route of it). The anime adaptation, on the other hand, is little short from being 6 hours long. It hardly takes a genius to figure out that something had to go.
* AdaptationExpansion: The anime introduces Ayase's cocytus-delusion, which functions as a freezing attack. Additionally, the events of episode 8 are anime-only.
* AffectionateNickname: Rimi always calls Takumi "Taku." [[spoiler:This is to differentiate between the two people she knows who call themselves "Takumi."]]
* AllJustADream: Some of the positive delusions try to provide a HappyEnding through this, Takumi even [[LampshadeHanging lampshades]] the cliche.
* AmplifierArtifact: Di-swords serve as these, allowing the Gigalomaniac to properly make use of their hallucinations. [[spoiler: Takumi is the only person who has been evidenced to do them without one.]]
* AngstySurvivingTwin: [[spoiler: Yua. Her twin sister [[ThemeTwinNaming Mia]] died in the "Group Dive," the ''first'' First Gen incident. Yua then launches her own investigation into [[ThemeTwinNaming Mia's]] death. She suspects Takumi is involved in the First Gen murders and pretends to befriend him under the ruse of being a [[GamerChick girl otaku]]. When Takumi finds out her true intentions, Yua ... [[NotHerself doesn't]] [[ScaryShinyGlasses take]] [[DepartmentOfRedundancyDepartment it well]]]].
* TheAnimeOfTheGame: The original PC game was released on August 26, 2008. The TwelveEpisodeAnime ran from October 9 to December 25, 2008.
* AnnoyingYoungerSibling: Nanami
* ArcWords: "Whose eyes are those eyes?" (''"Sono me, dare no me?"'') Even reaches memetic status in-universe.[[note]]Translated in the dub as "Those eyes...whose are they?"[[/note]]
* ArtificialHuman: [[spoiler:Takumi is a delusion given human form and artificial memories.]]
* BandOfBrothers: Takumi and his guild partner Grim [[spoiler: who turns out to be the one behind most of the new-gen killings.]]
* BeethovenWasAnAlienSpy : Einstein was a Gigalomaniac.
* {{BFS}}: The Di-Swords.
* BittersweetEnding: [[spoiler: Slightly more sweet that bitter, although the real Takumo is dead and Sena's father saved Sena at the cost of his own life, the un-real Takumo finally realizes and confesses his love for Rimi, all the members of his band are still alive, the world was saved and Kozue regained her normal, non-telepathic voice.]]
* BlandNameProduct: Deluoode for Google, and We-Key Pedophilia[[note]][[Wiki/{{Uncyclopedia}} the Encyclopedia of Useless Knowledge]][[/note]] - seriously - for TheOtherWiki.
** The list goes on, believe me - Taboo! (Yahoo!), Slavecard (Mastercard), Grouchosoft Mindorz X Perfect (Microsoft Windows XP Premium... seriously), THREE different [=McDonald's=] spoofs ([=McDeinald's=], [=McDynald's=] and [=WacTiKald's=]), Asos (Asus)... there are easily a half dozen of these in each chapter of the game, and the anime adds in even more.
** [=MewTube=] (Website/YouTube) and @-Channel (2-Channel).
*** ...both of which would later resurface (and play major roles in) ''SteinsGate''.
* BreakTheCutie: ''Every single heroine''. [[spoiler:It's the basic requirement to obtain a Di-Sword, after all...]]
* CallingYourAttacks: Subverted; in the only instance, the character can't think of a name to use
* CannotStandThemCannotLiveWithoutThem: Takumi's attitude towards "3-D" girls.
* CantYouReadTheSign?: @chan has a "20 years or older" rule, clearly seen every time Takumi (17) is reading it.
* CaptainErsatz: [[Franchise/StarWars Darth Spider]]
* CastFromLifespan: Any Gigalomaniac that overuses their powers risks severe damage to themselves. [[spoiler: Shogun is very far along with process, thanks to constant use of his powers along with his genetic disorder, and the creation of Takumi put him in a coma for a year.]]
* CharacterBlog: Part of the website for ''Chaos;Head Noah'' features blogs by each of the six main girls and one for Takumi.
* TheChessmaster: [[spoiler: Norose]].
* ChunkySalsaRule: Invoked. [[spoiler: And subverted. When Takumi learns to heal, he can grow a new head as easily as any other body part.]]
* ClapYourHandsIfYouBelieve: When a Gigalomaniac finds their Di-Sword, they gain the ability to Real Boot delusions. This forces others to perceive the delusion, giving it physical form.
* ClonesArePeopleToo: [[spoiler: Shogun considers Takumi to be a real person, just one who was born differently, and he wants Takumi to live on after his imminent death. In ending AA, Rimi agrees with Shogun.]]
* CombinationAttack: Gigalomaniacs can work together to Real Boot delusions, resulting in more powerful effects.
* ContinuityCameo: The name Neidhardt is mentioned in passing in SteinsGate.
** The diagrams showing how to control a peron's five senses are also used when the protagonists in SteinsGate attempt to [[spoiler: built a MentalTimeTravel machine.]]
** Neidhardt's ESO friend Geji-nee is referenced in Steins;Gate, where she coordinated an attempt by various @channers to locate the IBN5100, and more concretely in Robotics;Notes, where it's made clear that [[spoiler: she's an AI.]]
* CooldownHug: Rimi delivers one to Takumi when he starts having a breakdown on a middle of a road.
* CounterAttack: When two Gigalomaniacs fight, they can even turn a delusion against the original user.
** [[spoiler: When Suwa tries to catch Takumi in a delusion to keep him from defending himself, Takumi turns it around on him, forcing Suwa to kill himself.]]
** [[spoiler: When Norose uses a delusion that destroys Takumi's sense of himself as a human being, Takumi eventually embraces it, using the delusion to get around NoSelfBuffs.]]
* CruelAndUnusualDeath: The New Gen murders featuring a guy who was killedby having his blood drained and a guy killed by scooping his brain out with a spoon. However, the 2nd incident easily takes the cake ''and then some'' after you get know the circumstances of the murder. [[spoiler: Nurse Hazuki, who together with Suwa is the culprit behind all these cases, restrained the unlucky guy on a operating table and proceeded to vivisect him '''without any sort of anesthesia'''.]] And that isn't even the worst part. Remember that an unborn child was inserted into his body? [[spoiler: That's Hazuki's baby of whom Suwa is the father. How it got into that guy's body you ask? Well, after slicing the victim open, she - I shit you not - proceeded to cut her own womb open, rip the fetus out and shove into that guys stomach. And she did this '''without any anesthesia''', all while sprouting an SlasherSmile par excellence and mumbling stuff in some sort of trance.]]
* CuteAndPsycho: Two. Nice with some disturbing and murderous traits: [[spoiler:Kozue]]. Jerkass psychopath with a veneer of civility: [[spoiler:Suwa]].
* ColdBloodedTorture: A form of chinese water torture was done to [[spoiler:Ayase]] in her backstory.
* CuteMute: Kozue, at first.
* DepartmentOfRedundancyDepartment: [[spoiler:Serious-mode Yua]] has a habit of emphasizing sentences by repeating them several times in a row with slightly different phrasings.
* DeusSexMachina: Many of Takumi's delusions are about one of the girls randomly coming on to him.
* DiabolusExMachina: Route B is one huge ever-expanding example of this, featuring among other things, [[spoiler:a DespairEventHorizon (Sena) and BodyHorror AndIMustScream (Kozue), all of which culminates in a LetThemDieHappy MercyKill JustBeforeTheEnd for a ShootTheShaggyDog ending]]. And the reason why it all happened? [[spoiler:Kozue got knocked unconscious during the earthquake]].
* {{Dojikko}}: Kozue. Also Yua, in the anime.
* DontLookAtMe: Takumi has three notable instances of using this: First two times are near the end (or [[HowWeGotHere beginning]]), first one being directed towards The Gaze while the second one is for Rimi. Third one is addressed at pretty much everyone around him [[spoiler: after he was set up as an ESP]]. He never actually says them out loud though.
* DownerEnding: Endings A and B. The anime follows AA, the happy ending.
* DysfunctionJunction: We'll be here all day if we try listing all of the crazy in this show. It's pretty much a given that the gigalomaniacs are pretty broken at least.
* EleventhHourSuperpower:[[spoiler: When Takumi recovers from Gorose's attempt to destroy his whole entity, he has come in terms with being a delusional existence. This means that he can treat himself as one, which in turn makes him indestructible.]]
* EmotionlessGirl: Ayase.
* EvilPhone: At one point, Takumi gets a phone call from an out-of-service number, where he hears a creepy children's song followed by ambulance sirens and a near-deafening beep. [[spoiler: It's the sounds of Noah II starting up.]]
* {{Expospeak}}: Halfway through the anime they seem to replace the UnreliableNarrator stuff with massive amounts of technobabble.
** If you pay attention closely, [[FridgeBrilliance the technobabble is equally unreliable]]. Remember, [[DysfunctionJunction everyone in this show is certifiably insane.]]
* EyesAlwaysShut: Detective Ban's right eye is almost always closed, giving him a Series/{{Columbo}}-esqe appearance.
* {{Fanservice}}: Some of the delusions Takumi is having qualify for this.
** The rest tend to be FanDisservice.
* FakeBand: Phantasm. Their lead singer is FES, also known as Ayase Kishimoto.
* FictionalVideoGame: ''Empire Sweeper Online''
* FingerInTheMail: Happens when [[spoiler:Nanami]] gets kidnapped. Although instead of a finger, it's a whole hand.
* FirstPersonPerspective: In the visual novel. [[spoiler: *All* of the visual novel is first-person; Takumi sees everything the camera shows, though it takes him some time before he realizes this and accesses the knowledge.]]
* FlashForward: The show starts with one
* FlawedPrototype: [[spoiler: Takumi. Shogun couldn't afford to try again.]]
* FormulaicMagic: fun[[superscript:10]] int[[superscript:40]] = Ir2, [[spoiler:the equation Takumi discovered in elementary school and the basis of the Noah Project]] and is referred to as more revolutionary than e = mc[[superscript:2]]. What the equation actually signifies is never explained in depth.
* {{Geek}}: Takumi. [[spoiler: Yua acts like one to get Takumi to trust her.]]
* GirlWithPsychoWeapon: The entire core female cast.
* GoMadFromTheRevelation: Sena's mother. [[spoiler: She was secretly used as a test subject for creating matter from delusions artificially. Since her second child and Sena's little sister mana died shortly after birth, they created a new baby from artificial delusions and gave it to her. Sena's father was against turning her into a guinea pig, but also didn't want her to realize that her child had died, so he reluctantly approved. The experiment continued for several years, until it was decided that enough results were gathered from it and it will be halted. Sena (who didn't know about the experiment) unfortunately happened to be there when they turned the machines off, causing her mother to freak out upon realizing she's been carrying a corpse and proceeded to tear at her face, ''eat her child's corpse'', and stab her own eyes out with a pair of scissors. All while Sena could do nothing but watch.]] No wonder she hates her dad.
* GovernmentConspiracy: [[spoiler: While it turns out that it wasn't the mysterious 300 man committee behind the events but Norose and a couple of traitors from the committee, they still had a fair few companies and organizations working towards their aims.]]
* GratuitousEnglish: "New Gen" and a few others.
* HairColors: Fifty-fifty split - Rimi, Kozue and [[YouGottaHaveBlueHair Ayase]] have them, while Yua, Sena, and Nanami have more normal blonde and black shades.
* HandsomeLech: Takumi's best(/only) friend Misumi.
* HarmfulToMinors: Sena and her mother, sister and father. Wow.
* HealingFactor: Subverted. Gigalomaniacs can alter reality, but they can't use their powers to heal. [[spoiler: Eventually played straight with Takumi.]]
* HeroicBSOD: [[spoiler: Takumi has two during the course of the story. The first is after chapter 6, when he thinks his sister is dead. The second is after the revelation that he's an ArtificialHuman.]]
* HospitalHottie: Shino. Also a {{Meganekko}}, to an extent.
* HowWeGotHere: The story starts with Takumi lying in a ruined Tokyo street. Rimi creates a Di-Sword and kisses him just before she stabs him. [[spoiler: Subverted in the AA ending, where the sword wasn't Real Booted.]]
* ItsASmallNetAfterAll: Averted most of the time, there are random comments, spam e-mail, and useless search results.
* ImageSong: Each heroine has her own ImageSong that plays during the credits of her respective route in the XBox360 version of the VisualNovel
* ImaginaryFriend: Seira, from ''[[ShowWithinAShow Blood Tune]]''
* ImagineSpot: Defines Takumi's 'delusions', but it seems as though he doesn't remember them. Some might go into DaydreamSurprise territory, except they're obvious to the audience, particularly because you have to trigger them yourself in the game.
* InterruptedSuicide: [[spoiler:Ayase. Takumi's first conscious use of his delusionary abilities in the game is to create a flowerbed which breaks her fall after she attempts suicide by jumping off the roof of the school.]] And later on, [[spoiler:Takumi himself]].
* LighterAndSofter: ''Chaos;Head Love Chu Chu'', a true UnwantedHarem romantic comedy version that's actually a sort of sequel to the main series of events.
* LittleSisterHeroine: Several 'Delusion' events play up this angle, such as with the indirect kiss scene.
* LotusEaterMachine: [[spoiler:At the end of route B. Takumi didn't escape it.]]
* ManicPixieDreamGirl: Takumi hopes that Yua, and later Rimi are this.
* {{Meganekko}}: Yua, [[spoiler: [[NotHerself most]] [[ScaryShinyGlasses of the]] [[DepartmentOfRedundancyDepartment time]]]].
* MemeticMutation: [[{{Invoked}} Applied]]. After the release of the fourth New Gen murder, which had ''"Sono me, dare no me?"/"Whose eyes are those eyes?"'' written in blood, the entire city ended up repeating it.
* MindRape: Most of the delusions that NOAH II causes are psychological attacks, so this is to be expected.
* MindScrew: With Takumi leading the narrative, not only does he not have any idea what's going on, the audience doesn't know much more than he does.
** This happens from the gameplay perspective as well. Choosing a delusion trigger will show a flash of images, followed by the screen going slightly blurry, as a sign of Takumi having a delusion. As the game progresses, these indications won't always show up when a delusion is in progress; the player will know only after the game cuts them off in the usual manner. To make things even more confusing, delusion triggers sometimes trigger real events to happen to Takumi.
* TheMole: [[spoiler: Suwa]].
* MultipleEndings: Three ones in total.
* NinetyPercentOfYourBrain: Norose's reasoning for how the abilities of Gigalomaniacs work.
* NoSelfBuffs: Gigalomaniacs can't heal injuries with their powers. This is because their powers don't allow them to ignore the pain. [[spoiler: Subverted when Takumi learns to turn off his sense of pain.]]
* {{Otaku}}: Takumi. Specifically of the Anime sort, though he ''really'' likes his {{MMORPG}}.
* PoweredByAForsakenChild: Creating a Di-Sword for the first time requires a Gigalomaniac go undergo severe psychological trauma. [[spoiler: By extension, the perfection of Noah II required creating Gigalomaniacs and taking samples from them.]]
* ThePowerOfFriendship: [[spoiler: Takumi sees his six friends praying for his success and safe return while undergoing a delusion attack, motivating him to turn it around. This leads to his EleventhHourSuperpower.]]
* PsychicLink: [[spoiler:Kozue uses this to communicate telepathically. Kind of. It's stated that somehow it is entirely different because it runs off the power of delusions]].
** [[spoiler:Takumi and Shogun have one as well, mainly because they technically are the same person]]
* RapidAging: [[spoiler:Using the power of delusions apparently causes one to age faster. This is only relevant to Shogun who has a genetic disorder causing him to age faster. As a result he's almost dead of old age at the start of the story at about 17 years old.]]
* SeriousBusiness: Do NOT mess with Sena's popsicle.
* SharedMassHallucination: One of the central ideas in Chaos;Head, but it runs on the idea in reverse: if you can get more than one person to see the same thing (real or not), it becomes real. Whether it's explained as magic or science depends on the character given the explanation, although the story focuses more on the scientific one.
* ShoutOut:
** There is some talk about [[Franchise/StarWars a sci-fi movie series called ''Spark Wars'', in which the villain is a person in black mask called Darth Spider.]]
* ShowWithinAShow: ''Blood Tune''. All the audience really knows about it is lead character Seira, who Takumi is deluded enough to see talking to him.
* SlasherSmile: Used frequently in Takumi's bad delusions. [[spoiler: Norose starts sporting these frequently as well after he's been revealed to be the Big Bad.]]
* SplitPersonality: Takumi starts to think he had one that was responsible for the new gen killings. [[spoiler: He was completely wrong.]]
* 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.
** TheReveal of [[spoiler:Norose as the BigBad]] is also somewhat spoiled in the anime OP by the shot of [[spoiler:him grinning maniacally]].
** There's also the shot of [[spoiler:Hazuki and Suwa]] together... why would those two characters be even be associated? ...Oh...
* StrawNihilist: Norose.
* SuspiciouslyAproposMusic: In all three versions of ''Chaos; Head'', the music by Phantasm is not only apropos, it's plot important, since it seems to be predicting the New-Gen events.
* SurprisinglyGoodEnglish: The ending theme is about 75% this. The performer, Seira Kagamai, born to a French-Canadian father and a Japanese mother, is (obviously) fluent in both English and Japanese.
* SwordOfPlotAdvancement: After Ayase gives Takumi a cryptic offhand comment about Di-sword, he starts searching for it, if only to gain even some security in his current situation.
* TakingTheBullet: [[spoiler:Sena's father, Hatano to protect Sena from getting shot.]]
* TechnoBabble: Most of Takumi's encounters with Sena result in her explaining something about Gigalomaniacs in this manner.
* ThemeTwinNaming: [[spoiler: Yua and Mia]].
* ThisIsReality: Referenced rather frequently, but most often by Takumi himself
* TomatoInTheMirror: [[spoiler: Takumi is actually a delusion of...himself. The other him being what the protagonist him knows as "Shogun".]]
* TookALevelInBadass: Takumi does by the end.
* TrademarkFavoriteFood: Sena loves Crunchy-Kun popsicles.
** There's also Momose and her pronounced fondness for Japanese sweets.
* {{Tsundere}}: Sena. She even has a ShoutOut to [[ShakuganNoShana Shana]], Nanami also shows tsundere traits focusing on un-giver strategy
** And in one of the delusions, Takumi is called on his phone by an (otherwise nonexistent) incredibly generic Tsundere love interest, whose every second sentence is "It's not that I like you or anything".
** ''I Love Tsundere'' Music Player (Extras) - "I'll let you listen! But only because it's you."
* TwelveEpisodeAnime
* TwinSwitch: [[spoiler: The game and anime alike drop a lot of hints that the girl we know as Yua was actually her twin, Mia. The incident that gives her her Di-Sword has her conclude that it doesn't matter which one she is.]]
** [[spoiler: Her character route in the UpdatedRerelease confirms that they indeed switched places right before the incident. Because Mia suddenly didn't feel like attending an otaku meeting she was actually looking forward to (she's quite moody, to be exact), she convinced Yua of switching clothes so she can attend the meeting in Mia's stead.]]
* UltimateGamer386: The protagonist himself, too obvious.
* UnreliableNarrator - The start of the anime is entirely from the perspective of the delusional main character, and he's not sure what's going on.
** Everyone is an UnreliableNarrator in this show. Both the pseudo-scientific and pseudo-religious explanations are likely the results of each character's own delusions: [[spoiler: Sena, the main source of technobabble, is heavily influenced by the occupation of her father, which ties in directly to her incredibly traumatizing childhood; Ayase, who is the main source of the pseudo-spiritual explanation, is shown reading a book in the hospital entitled "The Knights OF Gradiale," her name for the Di-Sword wielders.]]
* UnwantedHarem: While [[spoiler:except for Rimi]] none of them are after Takumi romantically, elements of the genre are invoked in a fashion. Official art usually depicts Takumi with the six leading girls of the show in a way reminiscent of it as well.
** When Takumi [[spoiler:is being tortured in the final episode of the series]], he slips into a delusion of having a romantic comedy-like relationship with the girls.
* UpdatedRerelease: ''Chaos;Head Noah'', for the [=XBox=] 360. Changes to the game include adding routes for each of the girls and changing it to widescreen. [[spoiler: They also changed the route system; you now have to finish each route to unlock the True Ending, which can then be directly selected from the Main Menu.]]
* VirginPower
--> '' '''Takumi:''' [[InsultBackfire Earlier, you called me a Cherry-Boy.]] [[PreAssKickingOneLiner Did you know? Virgins have incredible imaginations!]]''
* WellIntentionedExtremist: Norose. The fact that he's also a StrawNihilist pursuing his goals to extremes tend to make him less than sympathetic, though.
* WrongGenreSavvy: Sometimes Takumi thinks of himself as a character in an RPG.
* YoungerThanTheyLook: [[spoiler: Shogun is a high school student. Takumi is a month and a half old.]]
* ZettaiRyouiki: Rimi and Kozue.

-->''Whose eyes... are those eyes?''