A mad scientist known as Key Man has created a rampaging virus that mutates unsuspecting humans into nightmarish abominations of nature, and in order to dispose of these repulsive monstrosities, the Tokyo police have created a special squad of fearless freak fighters. Chief among these brave officers is Ruka, a sword-swinging dealer of death who has a special knack for dispatching with Key Man's hideous creations. Despite the fact that they operate on opposite sides of the law, Key Man and Ruka have both dedicated their lives to one common goal: seeking vengeance against the crooked cops who killed both of their fathers many years ago.