Diana

Diana is also a guardian cat, sent from the future (Crystal Tokyo) with ChibiUsa. It is later revealed that she is Luna and Artemis' future daughter.
Mythology: Selene (Greek for "moon") was the Greeks' first goddess of the moon. The Roman version of Selene is Luna (Latin for moon) and the Roman version of Artemis is Diana... thus the names for the three cats (Luna, Artemis, and Diana).