Cardcaptor Sakura

Sakura Kinomoto was an ordinary 4th grader until the day she opened a strange book and let dozens of powerful magic cards loose on the world. Keroberos, the Guardian of the Clow Cards, informs Sakura that it is now her responsibility to find and capture the freed cards. However, much to the reluctant Sakura's dismay, things aren't going to be easy for her; simply saying magic words and waving her wand around isn't good enough. Each card is a living, thinking, extremely powerful being. She'll have to learn to cope with her new responsibilities, as well as ordinary troubles involving love, school, family, and friends. With the support of her friend Tomoyo and a young boy with powers of his own, she must learn how to use her newly awakened magical abilities to collect each card and prevent the disaster that will befall the world if she doesn't.

I have to say this is one of CLAMPS best shows. If you haven't seen it watch it and if you have re-watch it.