O-Parts Hunter, known as in Japan, is a Japanese manga series published by Enix (later Square Enix) under its Monthly Shōnen Gangan imprint, and created by Seishi Kishimoto, the younger twin brother of Masashi Kishimoto, creator of the highly popular manga series Naruto. The series draws heavily on Kabbalistic traditions and Judeo-Christian demonology for its plot, and less so on Japanese folklore. It is licensed for an English language release by Viz Media, which released it under the title to O-Parts Hunter. Since then end of 666 Satan Seishi has moved on to a new manga Blazer Drive
Ruby Crescent is an ordinary girl. Her life is changed dramatically when her father dies and she becomes a treasure hunter as he was. Her objective is to find O-Parts: magical items hidden in ruins which grant people superhuman powers and can only be used by an O.P.T. (O-Part Tactician), Angel, or Devil. She soon meets a mysterious boy named Jio 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. claiming 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 unlocking their pasts.
One of the two main antagonists of the series, they are the corrupt government who is led by Amaterasu Miko.
An 'underground' organization with the goal of getting rid of the Stea Republic, they are led by Jack Crescent.
Consists of:
As of the beginning of the time-skip all but four Angels have yet to be inserted into the Kabbalah, those four being Metatron, Zadkiel, Samuel, and Sandalphon.
| Angel | Number | Virtue | Symbol | Named After | Character | Status |
| Metatron | 1 | Crown | Metatron | Cross | Sealed | |
| Raziel | 2 | Wisdom | Raziel | Sealed | ||
| Jophiel | 3 | Intellect | Jophiel | Sealed | ||
| Zadkiel | 4 | Mercy | Zadkiel | Zero | Sealed | |
| Samael | 5 | Justice | Samael | Rock | Sealed | |
| Michael | 6 | Beauty | Michael | Mysterious Youth (clone) | Original: Sealed Clone: Destroyed | |
| Haniel | 7 | Eternity | Haniel | Sealed | ||
| Raphael | 8 | Glory | Raphael | Sealed | ||
| Gabriel | 9 | Foundation | Gabriel | Sealed | ||
| Sandalphon | 10 | Kingdom | Sandalphon | Ruby Lilly(clone) | Original: Sealed Clone: Destroyed |
| Demon | Number | Virtue | Symbol | Named After | Character | Status |
| Lucifer (Satan) | 1i | Atheism | Lucifer (Satan) | Jio | Destroyed (Absorbed by Jio) | |
| Beelzebub | 2i | Ignorance | Beelzebub | Ikaros | Sealed | |
| Lucifuge | 3i | Disinclination | Lucifuge | Yuria (Nucleus Removed) | Sealed | |
| Astaroth | 4i | Oblivion | Astaroth | Sealed | ||
| Asmodeus | 5i | Cruelty | Asmodai | Jack Crescent | Sealed | |
| Belphegor | 6i | Ugliness | Belphegor | Jack Crescent | Sealed | |
| Baal | 7i | Lust | Baal | Sealed | ||
| Adramelech | 8i | Avarice | Adramelech | Kujaku (Nucleus Removed) | Sealed | |
| Lilith | 9i | Chaos | Lilith | Ponzu(Nucleus Removed) | Sealed | |
| Naamah | 10i | Materialism | Naamah | Whale-like creature | Sealed |
O-Parts are 'artifacts' found throughout the world of O-Parts Hunter. They are mainly used as weapons and also as transportation for some people. the only people who are able to use O-Parts are people called O.P.T.(O-Part Tacticians), these people are able to release their 'spirit energy' and focus it into the O-Part, where in the O-Part then absorbs the spirit, then uses it as fuel to activate its effect which can range from fire to teleportation.
The series ended with 76 chapters separated into 19 published volumes. The manga itself was published by Square Enix under its Monthly Shōnen Gangan.