Urashima is an island located far from the mainland, where its inhabitants lead carefree lives. However, five years ago, the island's three great families endured a series of misfortunes and fell into suspicion. Consequently, the islanders severed all contact with the mainland, initiating a slow decline. The key to saving the island rests with three girls from these families, yet they are bound by old traditions and remain conflicted. On this island, a lone man washes ashore. Claiming to be from the future, he begins a solitary struggle to alter the island's fate.