Naotaka Hayashi (scenario writer)Choco (product designer)Toshimichi IsoeTakeshi Abo (composers)

EOCS:15+ (PC)

Chaos;Head (カオスヘッド, Kaosu Heddo?), stylized as ChäoS;HEAd, is a Japanese visual novel developed by 5pb. and Nitroplus that was released on April 25, 2008 for the PC. A port of the game, named Chaos;Head Noah (カオスヘッドノア, Kaosu Heddo Noa?), for the Xbox 360 console was released on February 26, 2009. The game is described by the development team as a "Delusional Science NVL" (妄想科学NVL, Mōsō Kagaku NVL?). The game's premise revolves around a high school student named Takumi Nishijō who unknowingly walks into the scene of a gruesome murder on his way home. More mysterious events starts happening afterwards as more gruesome murders occur in the area. Takumi struggles to cope with reality and the delusions he experiences as he tries to avoid getting caught by the perpetrator behind the chain of murders.

The game's story has been adapted into a manga that started serialization on May 21, 2008 in ASCII Media Works' shōnen manga magazine Dengeki Daioh. A second manga adaptation that focuses on Sena Aoi and Kozue Orihara began serialization in Media Factory's seinen manga magazine Monthly Comic Alive on August 28, 2008. It has been decided for this adaptation to be a side story to the original visual novel. A third adaptation begun serializing in Jive's shōnen manga magazine Comic Rush magazine on September 26, 2008. The anime adaptation of Chaos;Head was announced in the September 2008 issue of Comic Alive. The anime began airing in October 2008 and is produced by Madhouse.

The gameplay of Chaos;Head, like other visual novels, requires little player interaction as the game is primarily made up of text dialogues. The player only needs to read and click through the text to advance through the game. The text that is displayed on the screen depicts conversations between different characters or their thoughts.

Chaos;Head presents choices to the player through a unique "delusional trigger" (妄想トリガー, mōsō torigā?) system. This system presents the player with three choices relating to Takumi's psychological state. Two cardiac cycles will be displayed on the screen. A green, stable one will be on the top left hand corner and a red, unstable one will be on the top right hand corner. The third choice is not visible to the player as it requires no player interaction. The player may choose to click on the green or red cardiac cycle, or to simply proceed through the game without selecting either of them. The player is not required to make a choice immediately as the two cardiac cycles will remain on the screen until a predetermined number of lines has been passed since they appeared.

Selecting the cardiac cycles will often decide what kind of delusions Takumi will experience. The stable choice often shows a happy or humorous scene whereas the unstable choice will show very negative scenes possibly with gore and violence added. Yes and no questions also show up at times although they are much less frequent than the delusional triggers.

Chaos;Head primarily takes place in Shibuya, Tokyo. Many of Shibuya's physical locales like its busy pedestrian scramble and the Loft building appear in the game although their names have been altered slightly. Some notable Internet websites like Wikipedia, 2channel, YouTube, Google, and Yahoo! also show up in the game with modified names as We-Key Pedophiria, @-channel, MewTube, Deluoode, and Taboo!.

As the title implies, psychological themes relating to one's psyche and mind plays a large role in Chaos;Head. Delusions and the method of projecting one's own delusions onto the physical world, or onto someone else's visual system, is a key driver behind the story. Other scientific themes such as the concepts of matter, antimatter, and the Dirac sea are also brought up.

Chaos;Head's story is set in 2008 in Shibuya and is centered around Takumi Nishijō, a high school student at the private Suimei Academy, and the strange and brutal murders that have recently occurred in the Shibuya area, known as the "New Generation" (ニュージェネレーション?) Madness. The story begins on September 28 with Takumi talking to an online friend called Grim (グリム, Gurimu?). Grim is trying to bring Takumi up to speed about the recent New Generation events since Takumi is not interested in local or international news. A person named Shogun (将軍?) joins the chat room midway through Grim and Takumi's conversation. After Grim leaves the chat room, Shōgun begins to talk. He speaks in a very cryptic and confusing manner, leaving Takumi nervous. He then sends Takumi a barrage of image links, one of which appears to be of a brutal murder of a man being pinned by stakes to a wall.