Luna
Luna was found one day when Serena rescued the black cat from some kids. Luna followed Serena home and told her that she was Sailor Moon. Serena didn't believe Luna at first, but when she transformed, she realized it must be true. Luna is the most practical of all the cats. She guides Serena, Ami, Rei, and Lita. She turns into a human in the Sailor Moon R movie and falls in love with a man named Kakeru. Luna later realizes that she loves Artemis.
Luna-P
Chibi Usa's pet, that looks similar to a basketball with Luna's face.
Artemis
Artemis is Sailor Venus' guardian cat. Sailor Venus was originally Sailor V, who fought in London. Before Sailor Venus joins the rest of the Sailor Scouts, Artemis is the cat that Luna talks to secretly, through the computer at the video arcade. Artemis loves Luna. He would always watch over her, but Luna didn't realize that until later. Artemis also turns into a human to rescue Mina from a ledge she falls off of. Artemis was Mina's cat, before the existance of the Sailor Scouts. He gave Mina her transformation pen, so that she could fight the world's evils as Sailor V. Believing that the forces of the Negaverse would return to Earth, Artemis was an important guide to help Luna to find the other Sailor Scouts. Eventually he and Luna have a child named Diana who comes back from the future (just like Renie).
Diana
Diana is the grayish purple cat - Luna and Artemis' future kitten. In the anime, she comes in Sailor Moon S in place of Chibi-Usa's Luna Ball. She snuggles up at Artemis' side and says "Daddy." Artemis is confused, but when the Scouts hear this, they and Luna decide that Artemis had an affair with another cat and poor Artemis gets a big whack from Luna. Diana is Reni's guardian cat just like Luna is Serena's cat. She acts a lot like her mom and sometimes tries to discipline Reni as her mother does to Sailor Moon.
