Chaos;Head (ChäoS;HEAd, カオスヘッド, カオヘ) is the first main entry in the Science Adventure Series. It originally released for Windows PCs in 2008. It was originally described as a "Delusional Science Novel"—its expanded re-release, Chaos;Head NoAH, is described as a "Delusional Science Adventure," making it the first official entry in the Science Adventure Series.
Chaos;Head features psychological horror and mystery as its main themes. The gameplay revolves around the use of the "Delusion Trigger" system, which allows the protagonist to view positive delusions, negative delusions, or no delusions at all at various points in the story. In both Chaos;Head and Chaos;Head NoAH, the player's delusion choices may influence how the story progresses.
In 2009, an improved version of the game titled Chaos;Head NoAH was released for the Xbox 360. This version of the game featured new character routes, improved graphics, and various new story scenes. This version of the game was later ported to the PlayStation Portable, iOS, Android, the PlayStation 3, and the PlayStation Vita.
The direct sequel to Chaos;Head NoAH, titled Chaos;Head Love Chu☆Chu!, was released on March 25, 2010 for the Xbox 360, and was later ported to the PlayStation Portable, PlayStation 3, and PlayStation Vita. The game presents itself as a parody of other games in the dating simulator genre, and takes place during the summer after the events of Chaos;Head NoAH.
The thematic sequel to Chaos;Head NoAH, titled Chaos;Child, was released on December 18, 2014 for the Xbox One and later ported to the PlayStation 3, PlayStation 4, PlayStation Vita, Windows PC, iOS, and Android. The game shares several common elements, locations, and themes with Chaos;Head.
Chaos;Head canonically takes place in the year 2009 in Shibuya. The story follows Takumi Nishijou, a shut-in gamer and otaku that spends his days locked in his shipping container home playing video games, and only occasionally attending school based on his self-created "minimum attendance chart."
Unfortunately for Takumi, his peaceful days of NEETdom are about to come to an end. A mysterious stranger sends him a link to an image depicting a bizarre and gruesome murder scene, part of a recent serial murder case called the "New Generation Madness". As it turns out, the image that was sent to Takumi was of a murder that hadn't occurred yet. Takumi later stumbles across the murder scene as it is occurring in real life, and has an encounter with a girl who he believes to be the perpetrator.
Relation to Steins;Gate
Chaos;Head takes place in the same universe as the of the rest of the entries in the Science Adventure Series. Its expanded re-release, Chaos;Head NoAH, retcons the year the story takes place in to 2009, one year before the events of Steins;Gate.
Throughout the game, the player is introduced to numerous plot points and elements that later become significant to Steins;Gate. For example, the "Visual Rebuilding" (VR) technology introduced in Chaos;Head (and originally developed at Viktor Chondria University) is later revealed to be one of the main elements powering the Time Leap Machine in Steins;Gate, as well as the Amadeus system in Steins;Gate 0.
The Committee of 300, the overarching antagonist group of the series, are the puppeteers behind both Chaos;Head's N.O.Z.O.M.I. group and Steins;Gate's SERN group. Their goal in these and other Science Adventure Series titles is to cull the world's population to one billion and establish a "One World Government," through which they can rule the world.