Since 15 years ago, no new lives are born, and no one can die. And then, "gravekeepers" appeared in the world, with the ability to give rest to the living dead. Therefore the people said, "God abandoned the World". Ai who is 12 years old, one of "gravekeepers". Her life changes, when an immortal gunman named Hampnie Hambart murders the residents of her small village. She learns the "truth of world" from him, and decides to travel in order to save the world.