The "O-Parts Hunter" manga series, known as "666 Satan" in Japan, features a cast of characters created by Seishi Kishimoto. Set in the near future, it tells the story of a teenage girl named Ruby Crescent who wants to become a treasure hunter, following in the footsteps of her father. Her objective is to find O-Parts, ancient relics that can only be used by O.P.T.s (O-Part Tacticians), people who are able to release their Spirit and focus it into an O-Part to activate a special Effect, usually of a fantastic nature. She meets a mysterious boy named Jio Freed who, due to having a dark, lonely past, seeks to conquer the world. Jio is hostile to her at first but ends up traveling with Ruby as her bodyguard.