O-Parts Hunter, known as 666 Satan (Japanese: 666 ～サタン～, Hepburn: Roku-Roku-Roku Satan) in Japan, is a Japanese manga series written and illustrated by Seishi Kishimoto. It was originally published by Enix, who later became Square Enix, in their Monthly Shōnen Gangan magazine from 2001 and 2007, with the chapters collected into 19 tankōbon volumes. The series draws heavily from Kabbalistic traditions and Judeo-Christian demonology for its plot, and less so on Japanese folklore. 666 Satan has been released internationally in Spain, France, Italy and North America, although, Viz Media changed the title to O-Parts Hunter in the latter.

Plot

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: magical items hidden in ruins which grant people fantastical powers and can only be used by an O.P.T. (O-Part Tactician). She soon 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. When Ruby is attacked by an O.P.T., who claims to be Satan, Jio rushes to her rescue and a battle occurs. Initially they are on the losing side, but Jio releases his true power and is revealed to be not only an O.P.T., but the real Satan. Thus, the two continue to travel together in hopes of achieving their dreams.

O-Parts Hunter
Cover of the first manga volume
666 ～サタン～ (Roku-Roku-Roku Satan)
Genre	Adventure, comedy, fantasy
Manga
Written by	Seishi Kishimoto
Published by	Square Enix
English publisher	NA Viz Media Yen Press (digital)
Magazine	Monthly Shōnen Gangan
Demographic	Shōnen
Original run	2001 – 2007
Volumes	19 (List of volumes)