Yuni is one of the five main characters of Star☆Twinkle Pretty Cure who sometimes ends her phrases with nyan. Yuni's alter egos are Blue Cat, the phantom thief and Mao, the space idol. She is later able to transform into Cure Cosmo.

Yuni tends to prefer being a lone wolf and generally holds a strong responsibility for herself mainly rooted from her immense guilt of being unable to save her planet Rainbow, thus she rejects her friends' kind offers and assistance in the beginning and blames herself when she fails to accomplish her goals. Owing to her past career as Blue Cat, she has a bad habit of stealing as demonstrated in episode 22. Nonetheless, Yuni is still kindhearted, and she will still help and rescue the needy whether her foes or friends.

As Blue Cat, she is shown to be cunning by using the bright fireworks to make her break with the Princess Star Color Pen and Madoka's plan to use the star donuts as bargaining chips to win the pen at the Auction. According to Lala, she always gets what she seeks.

As Mao, she is very friendly and acts cutesy towards others. As it later turns out, it was merely an act she puts on to conceal her true identity as a thief.