Princess Rubina was an anime only character. She was the princess of and ambassador for the Amethyst Kingdom, and appeared only once, in the episode "Holiday in Juuban! A Carefree Princess."

Princess Rubina was first mentioned at the beginning of the episode when she was reported missing from her hotel before an international conference which was taking place in Tokyo. She first appeared before Usagi and Chibiusa as they were arguing over carrying packages, and inadvertently scared them away by performing a custom of her country in order to help them. However, she followed them to their house, and later accompanied them to a festival the two had planned to attend.

Though Rubina enjoyed the festival, she got into trouble when she gave balloons away without paying for them. After this debacle, she expressed her wish to be normal and free from being a princess, and then ran away. She eventually bumped into Mamoru, who reminded her that her people were worried about her, and also convinced her to stay with Usagi and Chibiusa for a little while longer in order to think about her decision.

Rubina attracted the attention of the Amazon Trio. Tiger's Eye called her "old" and refused to go after her mirror, so she ended up being attacked by Hawk's Eye. She was saved from him and the Lemures Elephanko by Sailor Moon, Sailor Chibi Moon and Tuxedo Mask, who then returned her to her embassy after the festival ended.

Princess Rubina longed to be free of her royal duties. She was shown to be slightly whimsical, and a little strange to most standards, but kind. As suggested by her actions in the episode, Princess Rubina was willing to help people out if she saw a problem.

Her kindness was unfortunately hindered by her country's customs (such as covering a man's mouth when she asks for help), which scared some people away from her. She was also hindered by a pure lack of street smarts; having been completely sheltered as a princess, Rubina lacked the ability to understand things such as money, privacy and even language, which also attracted undue attention.

(Source: Project WikiMoon)