But when Sakura opened it up, there was nothing left inside but Kero-chan, the book's cute little guardian beast, who informs Sakura that since the Clow cards seem to have escaped while he was asleep, it's now her job to capture them! Fourth-grader Sakura Kinomoto found a strange book in her father's library - a book made by the wizard Clow to store dangerous spirits sealed within a set of magical cards.