Clow Cards

In ancient times there was a powerful magician named Clow Reed. He was so powerful that he decided to create 52 cards, which he named the Clow Cards. When it was almost his time to pass away, he placed the cards into the Clow Book and put Cerberus the guardian on the front and Yue the judge on the back. Then he placed a magical seal on it so that only a person with magic can open the book.

When Sakura opened the book and released the cards they were scattered. They didn't have any owner so they were free to do anything. And they were really mischevious!! In order to seal a card, you need to make it weak or you need to bind its power. Then Sakura has to use the Sealing Staff to seal the card.

Once a card is sealed it doesn't belong to you unless you sealed its power. Even if Sakura used the Staff to seal it the card still might go to Syaoran or someone else if they sealed their power. After that the person who has the card must put their name on it.

Like in Episode 4 Sakura found 2 cards, Wood and Rain. And she forgot to put her names on them even though they were already in card form. So she went on an errand and when she came back the cards were activated!! And they were almost tearing her house apart. So it's important for the Card Captors to put their name on their cards.