Mau

The planet Mau is the home planet of the cats Artemis and Luna. Sailor Tin Nyanko also refers to the planet.

While neither the Anime or Manga elaborate on the planet; one can assume that the inhabitants are essentially 'Cat People'; able to take on the forms of both talking felines, and humanoids with feline features.
 * Diana is the only talking feline in the Anime or Manga that does not come from the planet Mau and was born on Earth.
 * All three guardian cats appear as humans at one point or another in the Manga while in the Anime the only one to appear in human form is Luna in Sailor Moon S: The Movie.