In the Land of Clow, teenage Syaoran returns from an archaeological dig excavating an ancient ruin, and is greeted by his old childhood friend, Princess Sakura. Sakura wants to confess her feelings for Syaoran, but is interrupted before she could do so.
Later, she meets Syaoran at the ruin. There her latent powers become active and wings (tsubasa) appear on her back as a mysterious person attempts to kidnap her. Syaoran prevents Sakura from being taken, but now Sakura is unconscious and her memories appear to be gone. She will die unless she can get help from the time-space witch Yuuko.
The priest-mage Yukito sends Syaoran across space and time to another universe where Yuuko resides. There, they not only meet Yuuko, but also Kurogane, a powerful ninja who was sent there by Princess Tomoyo from her universe to learn the true meaning of strength, and Fai, a powerful mage and creator of Chii in his world. He's on the run from a sleeping ruler named Ashura.
Yuuko agrees to grant all of their wishes, but at a heavy price. For Kurogane, he must give up his sword in order to travel through dimensions in the hopes of returning home. For Fai, he must give up the tattoos that his magic comes from so he can stay on the run. For Syaoran, he must give up his current relationship with Sakura to travel through the dimensions to find the feathers of her wings which contain her memories. And Sakura, though unconscious, must give up her memories of Syaoran.
Together, the four set off with the critter Mokona, who can locate Sakura's feathers, open doors between universes, and communicate with Yuuko when needed.
Episodes 1 to 26 are the first season. Episodes 27 and beyond are the second season.