Diana is a small, grey-furred kitten who makes her first appearance in the anime during the Sailor Moon SuperS season. She arrives from the 30th century, the era of Crystal Tokyo, and is revealed to be the future daughter of Luna and Artemis, the two guardian cats who serve the Sailor Guardians in the present day. Her introduction in the present is marked by a moment of lighthearted confusion when Artemis is mistakenly suspected of having an affair, as the existence of a kitten calling him father comes as a complete surprise to everyone, especially Luna.

In terms of personality, Diana is a blend of youthful traits and surprising maturity. She is portrayed as curious, polite, and eager to be helpful, yet she can also be a little timid in new situations. Despite her small size and relative inexperience, she demonstrates bravery and intelligence when the situation calls for it. As the designated guardian and advisor to Chibiusa, who is also known as the Small Lady, Diana is remarkably wise and reasonable for one so young. She is deeply respectful of proper titles and customs, consistently addressing Usagi and Mamoru with the honorific "sama" and referring to Chibiusa by her formal title, Small Lady, rather than by her nickname. This respect extends to her parents, whom she formally calls Mother and Father.

Diana's primary motivation for traveling to the past is twofold: to keep watch over Chibiusa and to gain real-life experience. Her role in the story is directly tied to Chibiusa, acting as her constant companion, advisor, and confidante. Much like how Luna guides Usagi and Artemis guides Minako, Diana provides counsel and support to the young future Sailor Guardian. She can often be seen resting atop Chibiusa's head or staying close by her side throughout the events of SuperS. Her key relationships are naturally with her parents, Luna and Artemis, and with Chibiusa, to whom she is fiercely loyal.

While Diana does not undergo a significant character arc or development in the SuperS anime, she remains a consistent and supportive presence. Her character is largely defined by her earnest nature and her dedication to her duty. Unlike in the original manga, where she has a more expanded role including the ability to take human form and guard the Space-Time Door, the anime version of Diana in SuperS is depicted solely as a small, speaking kitten without these additional abilities. Her most notable abilities include her capacity for human speech, which she is careful not to reveal to ordinary people, and her knowledge of the future, which she can occasionally draw upon to help the Sailor Guardians. She is also easily identifiable by the small jingle bell she wears on a collar around her neck, a feature that distinguishes her from her parents.