Luna is a talking cat that appears from the very beginning and advises Sailor Moon and the Sailor Soldiers as well as trains them. Throughout the anime, she lives with Usagi Serena and she is shown growing close to Artemis, another feline guardian who belongs to Aino Minako or Sailor Venus. And then, in Sailor Moon Super S, her daughter, Diana comes to the past to help out.
In the Anime
Luna discovers most of the Sailor Soldiers (Sailor Moon (character), Sailor Mercury, Sailor Mars, and Sailor Jupiter) during the first season. She awakens them all in order to locate the princess, and gives each of them a transformation device of some sort.
She also gives them useful advice in times of need.
In the Manga
In the manga, Tin Nyanko says that Luna is a creature of the planet Mau. This is not shown in the anime.
- Luna means moon in Latin and the many languages derived from it (e.g. Spanish, Italian, Romanian, Russian, Bulgarian).