Cerberus is the Guardian of the Seal of the Clow who was napping at the time Sakura Kinomoto breaks the Seal and unleashes the Clow Cards. Cerberus is one of two guardians of the Clow (created by Clow Reed), and one of his missions is to select the candidate to become the new master of the Cards.
In his miniature, borrowed form he resembles an orange plush toy with white wings. Because Sakura feels that he does not resemble a "Kerberos," she calls him "Kero-chan." He initially rejects the name (Kero is also the Japanese onomatopoeia for the sound a frog makes, a comparison he resents), but soon comes to embrace it once he gets to know Sakura. Kero-chan is bossy, demanding, and gluttonous, but he also genuinely cares about Sakura and believes that she will become the next Master of the Clow, acting as her guide to gather the Cards. His hobbies include playing video games (which he takes up when he finds the console in Sakura's room and develops great skill at) and eating snacks and sweets, even though he receives his energy from the sun and does not need to eat to survive.
Cerberus's true form resembles a winged lion, but in order for him to achieve this original form, Sakura must capture The Firey and The Earthy cards. In his true form he has jurisdiction over all things fire and earth, the elements from which he draws his power. The known Clow Cards under his jurisdiction are Light, Firey and Earthy, but also quite probably the Glow, the Flower, the Little, the Shot, the Power, the Sweet, the Shield and the Sand. He can also raise powerful magical barriers, use his wings as a shield, and breathe fire.
