Cerberus is the guardian of the mystical yet dangerous book of Clow cards. He is the guardian of the sun, one of the two duty bound to protect the powerful cards, and opposite of the lunar guardian, Yue. For several decades he was locked away in the book of the Clow, which held the cards upon the death of their previous master, Clow Reed, until a new master appeared to take hold of the cards and their guardians. Cerberus’s character first appears at the beginning of the series when this new master, Sakura Kinomoto, releases him from the book. Once Cerberus is awakened (he was napping on the front cover) and released from the book he discovers the Clow cards have vanished, and appoints Sakura the title of Cardcaptor, and sends her off to retrieve the cards. Cerberus’s major role in the first half of the story is to select the candidate to take up his old master’s footsteps and inherit the Clow Cards, and to aid the candidate in their task of collecting the now awakened cards. Once all of the cards are captured and the Cardcaptor’s name is written upon them, Cerberus’s chosen candidate is then judged on their worthiness to own the cards by the other guardian, Yue.