Dumpling Headcanon

Luna, Sailor Mau, and Sailor Tin Nyanko: (Inspired by previous Headcanon about Diana/Sailor Mau)

Luna & Sailor Mau are sisters, hence Luna’s high status in the Silver Millenium. Mau was in a volatile region of the galaxy, so it’s Senshi stayed there rather than travel as one of Serenity’s guardians, so Luna was sent in her stead. Had Sailor Galaxia not stolen the Mau star seed, Luna would’ve inherited it after her sister’s death, becoming Sailor Luna (as she did in PGSM). In Neo-Crystal Tokyo, Luna briefly becomes Sailor Mau after the Black Moon Clan (more likely Wiseman acting on his own) kills her sister, thus alerting them to the threat headed toward them. Diana, being the daughter of a soldier initially acts as a sort of Sailor Mini-Mau, but soon Luna realizes that she hasn’t had the training necessary to be a soldier, and passes the mantle onto Diana, who is still young enough to learn the ways of a Senshi.

Another thing I’ve always liked to believe was that, in addition to retaining Saturn for her Sailor Team, Chibiusa convinced Neo-Queen Serenity to use the Silver Crystal to grant a Sailor Crystal and human form to Diana to make her the new Sailor Mau. If, in her weaker state as Super Sailor Moon she could grant Luna a temporary human form, it always seemed like an oversight that her advisors (and some of her closest friends) would stay cats in Crystal Tokyo.