In the not too distant future, mankind battles over O-Parts, powerful relics from an ancient civilization. Jio is a young boy with a tragic past who only trusts one thing in the world: money. Little does he suspect that he is also a very powerful O-Parts Tactician (O.P.T.), and inside him sleeps a demon of incredible ferocity. With his partner, Ruby, Jio embarks on a dangerous quest to acquire as many O-Parts as he can.
Although Ruby has succeeded in saving Jio's mind from the depths of Satan, her soul remains inside Satan/Jio's body. Realizing that Jio has come back, Cross decides not to kill him. But amid the turmoil, Ruby's pendant falls into Jio's hands...and Ruby's body (without her soul) falls into the Stea Government's!