The Tokyo area has been hit by a gigantic earthquake. In the midst of this chaos, Akito and Yumi meet and together they start traveling through the city in order to survive.

In an postapocalyptic world practically covered with water, Wadatsumi, a tomboy who lives in what she thinks to be the last piece of earth, knows a mysterious girl who was dragged by the waves of the sea.
Where did she come from? Are there more zones of earth in the world?