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.
Throughout the world, there are ten Angels and ten Demons with amazing powers, some of which are sealed within humans. They are being searched for by the Stea Government (Angels) and the Zenom Syndicate (Demons) who want to insert them within the Kabbalah and Reverse Kabbalah, that are found on the North and South Pole respectively. A legend tells that when either Kabbalah is filled, a super weapon called the Legendary O-Part will be awoken.