Known as "Chao" in Japan, Katy is a female cat created by Osamu Tezuka and Sanrio for the Unico manga series that ran from November 1976 till 1979. Debuting in "The Cat on the Broomstick" chapter, she wishes to become a "Cat Witch" after getting abandoned by her human owners but later decides to become a human girl. Unico decides to grant her wish by making her a human for a short period of time each passing day. In the 1981 movie, she becomes a human permanently after performing a selfless act by rescuing an old lady (known as either "Granny", "The Old Lady" and "The Old Begger Women" in the manga) from drowning with Unico's help.

In the English-language manga reboot series, she's known as "Chloe" debuting in the series' first volume "Unico: Awakening". In the reboot, she's a city watch cat who watches over animals similar to patrol officers. After witnessing Unico being chased by strangers, she rescues him from a city lake and takes him to her owner's apartment to dry off.