Diana is the daughter of Luna and Artemis as well as the Guardian of Chibi Usa. In the anime, she appears in Sailor Moon Super S from the future. Apparently, she has come to the present in order to not only keep an eye on Chibi-Usa, but to gain real-life experience. Diana appears to be small, sometimes timid but at the same time brave and smart. Her being Chibi-Usa's Guardian, she is also very wise and is often very reasonable. Despite her parents mentioning that she doesn't know very much about the 20th century and what she shouldn't do (such as exposing to other human beings that she has the ability to speak), she is well aware of the rules of being in society.
In the manga, Tin Nyanko says that they are creatures from the planet Mau. This is never mentioned in the anime.
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