The show begins as a simple girls' anime of the magical girl genre. Ten-year-old Sakura Kinomoto opens a mysterious book in her father's study and accidentally lets loose the magical Clow Cards. By her ability to open the seal, Sakura is revealed to have special powers, and it becomes her responsibility to retrieve the missing cards. The task involves finding each card, battling its magical personification, and sealing it away. She is assisted by Cerberus (Kerberos, also known as Kero-chan), the Beast of the Seal assigned to protect the cards, who was asleep when Sakura opened the Clow Book (He was on a "nap" at the time, which lasted 30 years). Kero-chan, who looks like an animated plush toy throughout most of the series (his "borrowed" form), guides Sakura as she develops her Cardcaptor powers. In the first episode, he presents her with the Key of the Seal, which allows her to fight and capture the Clow Cards.