Cardcaptor Sakura takes place in the fictional Japanese city of Tomoeda which is somewhere near Tokyo. Ten-year-old Sakura Kinomoto accidentally releases a set of magical cards known as Clow Cards from a book in her basement created and named after the sorcerer Clow Reed. Each card has its own unique ability and can assume an alternate form when activated. The guardian of the cards, Cerberus (nicknamed Kero), emerges from the book and explains that only a person with magical powers could open the seal of the book, clarifying that Sakura can do magic. Kero chooses Sakura to retrieve the missing cards. As she finds each card, she battles its magical personification and defeats it by sealing it away. Cerberus acts as her guide, while her best friend and second cousin, Tomoyo Daidouji films her exploits and provides her with both battle costumes and moral support. Sakura's older brother Toya Kinomoto watches over her, while pretending that he is unaware of what is going on.
Syaoran Li, a boy Sakura's age and a descendant of Clow Reed, arrives from Hong Kong to recapture the cards himself. While initially antagonistic, he comes to respect Sakura and begins aiding her in capturing the cards. Once Sakura captures all of the cards, she is tested by Yue, the cards' second guardian, to determine if she is worthy of becoming the cards' true master; Yue is also the true form of Yukito Tsukishiro, Toya's best friend who Sakura has a crush on. Aided by her school teacher Kaho Mizuki, Sakura passes the test and becomes the new master of the Clow Cards.