In a post-apocalyptic world covered with water, Wadatsumi, a person who lives in what appears to be the last piece of land, finds a mysterious girl dragged by the waves of the sea. Where does she come from? Are there other lands in this world?

After 'The Great Sinking,' civilization on Earth crumbled as the world was drowned in the ocean. One tiny band of survivors eke out a living atop the ruined remains of a skyscraper. Wadatsumi, a young tomboy, is saddled with the care of four elderly gentlemen, until a chance encounter with a group of pirates and a mysterious woman turn her world upside-down.