In the not too distant future, mankind fights over relics from an ancient civilization called O-Parts, each of which contain incredible powers. Some people with special abilities are able to use the O-Parts to their full potential, and are known as O.P.T.s (or O-Parts Tacticians). Naturally, O-Parts can be used for both good and evil purposes. 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 actually a very powerful O.P.T.s, and inside him sleeps a demon of incredible ferocity. He meets up with a girl named Ruby who, like her famous father before her, wants to become a treasure hunter. Though Jio doesn't believe in friendship, he agrees to be Ruby's bodyguard, and together they go on a dangerous quest to discover as many O-Parts as they can.