Name: 月 (yu-eh)
Birthday: Secret

Favorite Thing: Sleep
Least Favorite Thing: Anything troublesome
Favorite Food: Nothing (Yue doesn't eat anything)

Master/Mistress: Clow Reed, later Kinomoto Sakura
Symbol: Moon
Attribute: Darkness (The yin half of yin & yang)
Magical Power: Eastern Magic

First appearance (Anime): Episode 45, "Sakura and the Last Clow Card"
First appearance (Manga): Volume 6, Chapter 26 (Chapter 4 of Volume 6)

Yue is the other guardian of the Clow, that works alongside Cerberus as not only a balance to Cerberus' power, but also in a duties aspect. Where Cerberus is the elector of the new Cardcaptor, Yue judges the one that Cerberus has chosen. In other words, Yue is the Judge of the new Cardcaptor. In addition, Yue is the balance to Cerberus in almost every aspect - as where Cerberus is the cheerful, hyper one, he is the more serious and the calmer of the two. But despite his exterior, Yue is very kind and is compassionate the same way Cerberus is.

Syaoran also mentioned that while Cerberus has been recorded of in magical books and the such, not much is known about Yue, since he has a role later on in a Cardcaptor's journey. Yue remains a mystery to Sakura and her friends, but Kero-chan knows that sooner or later, the truth has to be revealed...