A high school student finds themselves in a place called The Cage — row upon row of towers built from stone and iron stretching in every direction. Mysterious creatures appear and offer to help navigate the place. The task they describe is specific: repair the sun or moon hanging in the air above. That is the condition for getting back to Tokyo. The student is uneasy. They press forward anyway, because there is a place they belong and they intend to get back to it.