She has white fur, blue eyes, and wears a pink ribbon around her neck.
The Cat Returns
Yuki first appeared as a stray kitten in a flashback, where she was seen being given fish crackers by Haru. In the present day, having noticed that something isn't right, Yuki, in a loud overarching voice, instructed Haru to seek the Cat Business Office, where she meets Muta, a large white cat Yuki told her to seek for directions, who leads her there to meet Baron Humbert von Gikkingen.
As Haru and Muta arrived at the Cat Kingdom, Yuki pleads Haru to leave the realm at once, only for Haru and Muta to be taken by the King's servants. It is then later revealed that Yuki works as a lowly servant at the palace, serving food and wine to the guests at the banquet. In the ensuing scuffle as the Baron is discovered, Yuki aids Haru, Muta and the Baron by leading them to an escape tunnel, where the three move through a maze to a tower, which contains a portal to Haru's world.
Lune and his guards then arrive at the Cat Kingdom, only to reveal that the Cat King isn't working on his behalf, and is intent on proposing to Yuki.