Kero is an adorable little flying lion type creature. He is the creature of the seal and is supposed to guard the Clow cards. He falls asleep for about 30 years and Sakura releases the cards. Kero looks out for Sakura. He loves playing video games and eating sweet treats. He has some magical powers, but won't be at full magical power until Sakura captures all the elemental cards: The Watery, Windy, Fire, and Earthy. In his true form he looks kinda like a lion with wings.

Kerberos isn't much different personality wise in his true form. He may be bit more serious but throws his weight around, literally, when he wants something.