The island of Urashima sits on the ocean far, far away from the mainland. The island is so lush and beautiful that one might mistake it for paradise, but the people there are trapped by a complex past and long-established traditions. Long since abandoned and all but forgotten by the mainland, the people of the island are ready to give up hope. But then, a young man named Setsuna who calls himself a "time traveler" washes up on the island. Setsuna has lost all of his memories except for a certain mission that he must fulfill. On Urashima he meets three girls, Rinne, Karen, and Sara, and begins.