Card Captor Sakura (aka CCS, aka Cardcaptors) is a Magical Girl (Mahou Shoujo) series created by CLAMP. Sakura, a 10 year old girl, open a magic book she finds in her basement, scattering the Cards that were locked inside. Soon afterwards Kerberos, the Beast of the Seal, floats out of the book, and freaks out when he finds Cards are gone (he's the guardian of the Cards, but was asleep on the job). So he tricks Sakura into becoming the Card Captor, the one who will return the cards to the book, since if the Cards are left free they shall wreak evil on the world.