Osamu Kogure is a young man who's out of prison and lives in poverty in an abandoned house, working odd jobs to survive. One day, his abusive prison senpai Inui arrives to boss him around. Inui makes Osamu reveal the location of his old girlfriend Koyuki, who he kidnaps, beats and rapes. When a robbery that Inui has planned goes wrong, Osamu's left arm is cut off. Koyuki takes him to a yakuza-affiliated doctor who treats him with an experimental medicine that regenerates his arm back as a monst...