A science fiction piece set in modern Japan. An alien parasite that survives by feeding on the brain of mammals arrives on earth. The creatures can change shape freely and are almost undetectable. One of the parasites attacks Shinichi Izumi, a high school student, but manages to control only Shinichi's right hand. The two are forced to co-exist and fight other parasites in order to protect each other. This is not only an action comic, but also probes deeply into the human psyche.