Setsuna washes ashore on Urashima, an isolated tropical island, with no memory of his name or where he came from, certain only that he is a time traveler sent to save a girl. He takes the name from a song he hears Rinne Ohara singing. Five years earlier the island's three founding families fell into mutual distrust and cut Urashima off from the mainland; his mission centers on Rinne, Karen, and Sara, the daughters tied to those families.