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 followed by releases on the PlayStation Portable, iOS, Android, PlayStation 3 & PlayStation Vita. The game is the first in 5pb.'s Science Adventure series, and 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. Although no release outside of Japan is planned, an unofficial English fan translation has been released.
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 to avoid trademark issues, and as jokes, as We-Key Pedophiria, , 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.