Inuyashiki Ichiro is an older, friendless man with an uncaring family. One fateful evening in a nearly empty public park, he is struck by an explosion of extraterrestrial origin, and his body is replaced by an incredibly powerful, but still outwardly human, mechanical body. He quickly realizes the extent of his body's powers, and after saving a homeless man being beaten by a pack of teenagers, he decides to dedicate himself to doing good, using his powers to heal those with incurable diseases and fight crime.

However, you, a teenager who was with him at the time of the explosion had the same fate as the old man, but unlike Inuyashiki, you become a psychopath who goes about using your newfound abilities to murder various people, from classmates that annoy you to innocent families, including young children, just for amusement.