On a secluded island distant from the mainland called Urashima, a man arrives on shore with no memory of his name or origin. He does remember that he is a traveler through time, tasked with rescuing a particular girl from danger. When night falls, he encounters Rinne Ohara, a young woman whose song evokes the name Setsuna in him, and he adopts that name for himself. Rinne herself knows another person named Setsuna, so she brings him into her home as a servant, hoping he is the one she recalls. Meanwhile, Setsuna keeps studying Urashima, eager to uncover his lost history. He learns of the island"s legends, its three prominent families, and a local illness that forbids sufferers from stepping into daylight. As the puzzles of his forgotten past and Urashima"s secrets unravel, Setsuna must recall his mission and act swiftly. Yet as he observes the island"s many hardships, he wonders whether his time shift is simply a bid to alter one girl"s destiny.
