The overarching plot of "Cardcaptor Sakura" is driven by the machinations of the deceased sorcerer, Clow Reed. The entire ordeal of scattering and recapturing the cards was a trial designed by him to find a worthy new master. The primary twist in the second half of the series is the revelation that the new transfer student, Eriol Hiiragizawa, is the reincarnation of Clow Reed himself. He, along with his guardians Spinel Sun and Ruby Moon (in the forms of Suppi and Nakuru Akizuki), orchestrated all the strange happenings in Tomoeda to force Sakura to transform the Clow Cards into Sakura Cards. This was necessary because the cards, tied to Clow's magic, would eventually die without a new master to sustain them with their own power.
Another major reveal is the true nature of Yukito Tsukishiro. He is not a normal human but a temporary form created by Yue, the Moon Guardian, to exist in the world. Yue, the Judge of the Cardcaptor candidate, was deeply devoted to Clow Reed and initially refused to accept Sakura as his new master. Yukito's existence becomes endangered as Sakura's power is not yet strong enough to sustain him. In a pivotal moment, Sakura's brother Touya reveals he has known about everyone's magical identities all along and willingly gives all of his own magical power to Yue to save Yukito's life, a sacrifice born of his deep love for him. Finally, Sakura's father, Fujitaka Kinomoto, is revealed to be the other half of Clow Reed's reincarnation. This explains why he was drawn to Sakura's mother, Nadeshiko, and why Sakura possesses such immense magical potential. Clow split his soul so that one half (Eriol) would retain his memories and magic, while the other (Fujitaka) could live a normal life without such burdens.