A seemingly impregnable and unassailable demon king's castle that towers high into the sky, and a kitten that can no longer come down from its roof.

In order to bring peace to the world, the hero Mars and the sage Cleo challenge the impregnable Demon King's Castle that towers high in the distant sky. In the great hundred-layered labyrinth, Mars and Cleo struggle against the hordes of demons. Meanwhile, the Demon King waiting for the hero on the throne at the top of the castle finds a kitten that has become unable to get down from the castle's roof. When the fates of both parties intersect, the story begins.