Based on a Japanese visual novel developed by 5bp and Nitroplus, Chaos;Head is a delusional murder mystery story, with strong elements of gore, psychology and science fiction. The game uses a feature called a “delusional trigger”, which allows the player adjust the ‘realness’ or ‘surrealness’ of the perspective of the main character, which directly affects the storyline.
The main character, Takumi is a troubled young man who struggles to distinguish reality from his delusions, while being pursued by the perpetrator of a series of bloody murders, (or so he thinks). His travels take him in and around Shibuya, Tokyo and his adventures bring him in contact with various scientific themes such as the concepts of matter, antimatter, and the Dirac sea.
Descriptions taken from AniDB.net