666 Satan (Japanese: 666 ～サタン～, Hepburn: Roku-Roku-Roku Satan), released in North America as O-Parts Hunter, is a Japanese shonen manga series written and illustrated by Seishi Kishimoto (the twin brother of Naruto creator Masashi Kishimoto). Serialized from 2001 to 2007, the series is known for its heavy use of Judeo-Christian demonology and Kabbalistic themes within a high-octane treasure-hunting setting.

The story is set in a world filled with O-Parts—ancient magical artifacts that grant superhuman powers but can only be wielded by specialized warriors known as O.P.T.s (O-Part Tacticians). The plot follows Jio Freed, a lonely and distrustful young boy with a dark past whose only dream is to conquer the world so that no one can ever look down on him again. He joins forces with Ruby Crescent, a determined young treasure hunter following in her father's footsteps. As they travel together, it is revealed that Jio's body serves as a host for Satan, a terrifying entity of immense power. Jio must navigate a world of shifting alliances and global conspiracies as he struggles to control the monster within and decide whether he will become the world's destroyer or its savior.

Alternative Names by Language

666〜サタン〜 / O-Parts Hunter / 666 Satan / 666 Сатана / ۶۶۶ شیطان / ۶۶۶ ساتان / 666 ซาตาน / 666 Сатан / 六六六撒旦 / 666사탄 / 666 సాతాను / 666 സാത്താൻ