There are two Earths, Hope Earth and Dark Earth. In the middle of a war, Light has smuggled the royal heir of Dark Earth to the peaceful Hope Earth, and is leading an ordinary school life while taking care of the young prince. He meets a young boy at a park named Ion, who he learns from Listel, a dear friend who is now a member of the opposing force, is Light's twin brother. And that Light and Ion's fated meeting were their thirteenth birthdays...