Chaos;Head 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 start 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 by Madhouse aired in Japan between October 9, 2008 and December 25, 2008.
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.
The next day, Takumi comes across a real life murder scene. Witnessing a mysterious pink-haired girl pinning a man up by stakes in an alleyway, he immediately realizes he is witnessing the very murder detailed in the pictures he received the day before. Convinced Shogun is targeting him and the girl he saw committing the murder is somehow connected to him, Takumi tries to avoid getting involved with other New Generation events. However, as Takumi begins attempting to distance himself from the crime he witnessed, he soon catches interest of the police.
With the police suspecting him, and himself convinced that he is being targeted by Shogun, Takumi finds himself caught in a spiral of delusions and paranoia, as he desperately tries to keep himself safe and figure out why he is apparently being targeted. He eventually comes into contact with several other people related to the events, including the girl he saw committing the murder herself. Unsure of what is real or who he can trust, Takumi finds himself thrust into a much larger scheme than he ever thought possible, as the mysterious company NOZOMI carefully plots something from behind the scenes.