Luna is a black cat and a major character throughtout the series.
Luna first appears in episode one. In the first scene she appears in, Usagi accidentally steps on her. After realizing what she did, Usagi fawns over her, apologizes, and removes the bandages covering the crescent moon symbol on Luna's head. They then stare at each other for a moment until Usagi realizes that she is late to school and leaves. Later when Usagi is at Game Center Crown, Luna sees her again. Finally, she appears once again in Usagi's room and wakes up Usagi, who was sleeping at the time, by scratching her face. When Usagi is awakened, Luna tells her that she is destined to become a Sailor Senshi and gives Usagi the brooch that allows Usagi to transform into Sailor Moon. After Usagi transforms, Luna leads her to where Morga is. During Sailor Moon and Morga's fight, Luna gives Sailor Moon tips on what to do to harm her enemy and teaches her a new attack called Moon Tiara Boomerang. At the end of the episode, Luna is seen with Usagi, who realizes that the events from the day before actually happened and that she wasn't dreaming.