Tsuki is the natural satellite of the planet Terra'su, and is considered one of the worlds of the Amaterasu System, with its population of Moon Rabbits, led by a sort of monarchy descended from the deity Tsukiyomi after his exile from his ex-wife, Amaterasu. It is home to the Myobu of Ocean, and has somehow avoided being conquered with the world it orbits, likely due to illusion magic preventing the Jupiter Empire from truly seeing where the Moon Rabbits cities are.