The anime takes place in the year 22 HC (Holy Century), in the Tokyo ward of Shinjuku. Although theoretically about the competition of rival private police corporations (licensed bounty hunting firms) in an Earth where humanity is in danger of extinction, in actuality it focuses more on the lives of the main characters, such as; Natsuki Sasahara, Sakura Bokuseiinmonzeninari, and Batanen Fujioka. The monsters are usually taken from Japanese mythology, updated for the modern era. In the anime, repeat criminal offenders in Tokyo have their memories wiped. However, in the manga version, they are castrated. Mithril exists in this world/setting; it is a sort of specially enchanted silver that is especially effective towards supernatural characters.