Chaos;Head (カオスヘッド Kaosu Heddo), stylized as Chäos;HEAd, is a Japanese visual novel developed by 5pb. and Nitroplus with gore, psychology, and science fiction elements 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.

Anime: Takumi is a high school student. He is withdrawn and is not interested in 3D things. In his town, a mysterious serial murder case happens and people get panicked. One day, when he chats on the internet, a man suddenly contacts him and gives him an URL. He goes to the website and finds a blog image that suggests a next murder case.... On the next day, it really happens....
Takumi Nishijō suffers from intense delusions as a result of his apparent schizophrenia and the extremely secluded lifestyle he lives as a hikkikomori. One day he accidentally stumbles upon a gruesome murder scene, a part of a chain of events called "New Generation." After this, his life gets caught up in these events, and he meets a bunch of increasingly insane anime girls with swords.

(source: Wikipedia, ANN)