Kinomoto Sakura is appointed Card Captor by the Guardian of the Seal, Cerberus, when she accidentally opens the magical book of Clow Cards and scatters them to the four winds. To protect the world from disaster she must capture all of the Clow Cards with the help of her friend Tomoyo and Cerberus.

[Source: AniDB]

It's winter vacation and Sakura wins a trip to Hong Kong. Kero, skeptic of her luck in lotteries, questions whether she was merely lucky or was she summoned to Hong Kong upon inevitability. As Sakura strolls through Hong Kong's Bird Street, she senses an evil force calling to her. On chasing two strange birds, she is lead to a phantom world where she learns she was actually made to come to Hong Kong by a woman, Madoushi, who apparently wants revenge on Clow Reed. With Syaoran's mother, Yelan's help and the guidance from Clow Reed's voice, she must fight Madoushi and rescue her friends and loved ones, who have been captured.

Following the events of Cardcaptor Sakura Movie 2: The Sealed Card, Kero and Spinel share a plate of takoyaki (octopus balls). They get into a fight over who gets the last piece, and in the process send it flying out the window. They both chase the takoyaki, and each other, in a mighty effort to be the "takoyaki captor".

[Source: Anime News Network]

During the Summer holidays, Sakura and her class are preparing to present a play at the annual Nadeshiko Festival. The unexpected arrival of Syaoran (and Meiling) give Sakura the courage to finally reciprocate her feelings. But as the cards begin to disappear one by one, Sakura discovers a single card still remains. One with power equal to all hers... It is during this summer that Sakura faces her final battle.

After the conclusion of the Sakura Card Arc, life is going back to normal. There are no more mysteries, no more disturbances of evil, no more tests of strength. Everyone is moving on with their lives and Sakura feels a sadness in her heart. Even through the goodbyes, Sakura perseveres to keep everyone and a special someone, dear to her heart.

[Source: MyAnimeList]

Fourteen-year-old Sakura starts junior high school along her friends, including Syaoran, who had just returned to Tomoeda. After having a dream with a mysterious cloaked figure, all of Sakura's cards turn blank and are rendered powerless, thus she starts her quest to find out what is wrong. In doing so, Sakura and her allies discover and capture new transparent cards using a new key.

[Source: Cardcaptor Sakura Wikia]