After the noble Kappa Kingdom falls to the Otter Empire, the Kappa prince Keppi loses much of his power and becomes helpless against the unseen Kapa-zombies. These zombies plague the world, and are the creations of the Otters and manifestations of people's deepest desires. With no other choice, Keppi must rely on three young boys: Kazuki Yasaka, who must carry a box with him wherever he goes; Enta Jinnai, Kazuki's ch...