Caty, originally named Chao, is a black-and-white cat appearing in multiple Unico stories. Abandoned by former owners for perceived clumsiness, Caty yearns to become a witch's apprentice, believing this magical association will earn her human respect and better treatment following past mistreatment.

Her story begins in the manga chapter "The Cat in The Broomstick," where she first encounters Unico after rescuing him from mud. Seeking magical training, Caty takes shelter with an elderly woman she mistakes for a witch. Unico secretly grants Caty's wish for temporary human form. However, observing her growing selfishness and neglect of the elderly woman, Unico revokes the transformation. Caty redeems herself by rescuing the woman from drowning. Recognizing this selfless act, Unico restores her human form permanently. This form typically features a dress, depicted as black with red accents in the manga and pink in the 1981 film adaptation.

The reboot series reveals additional background: Caty initially serves as a city watch cat, mentored by another cat named Lily. She rescues Unico from drowning, shares her history of abandonment, and departs with him. During their journey, she develops romantic feelings for another cat named Toast. After Unico leaves, Caty and Toast remain together caring for the elderly woman, now possessing the ability to shift between cat and human forms at will.

Across all versions, Caty displays a naive yet fundamentally kind-hearted nature. Her character consistently evolves from initial self-centeredness towards compassion and responsibility, particularly shown through her caregiving for the elderly woman. Physical attributes include distinct black-and-white fur, a signature red bow accessory (varying in placement between neck and head across media), and occasional depiction of whiskers in the reboot.