Card Captor Sakura

Cardcaptor Sakura is a manga series by CLAMP. The series' main character, Sakura Kinomoto, accidentally releases the Clow Cards--powerful magical items--and must attempt to retrieve them. This is more complicated than it sounds, though, since the cards fight back.

Tsubasa: Reservoir Chronicle, another work form CLAMP, is heavily canon related to CCS, since most of the main characters are Alternate Universe alter-egos of CCS ones, and the original Sakura also has an important part in the plot. So, any heavy attack on Card Captor Sakura's canon is likely to corrupt Tsubasa Reservoir Chronicle's one, if not even preventing the whole plot from happening.

Missions in this Continuum
Janet Ackerly and Cygna Hoshiko Sergio Turbo and Corolla
 * Love's Destiny
 * Lavender Shadow
 * Don't Forget the Canon