This lively little character is Kerboros, he shows up in episode one as the Guardian Beast of the Seal. Do to his careless nature he fell asleep and took a 30 year nap. (talk about your beauty sleep!) Because of this he can`t stop Sakura from accidently activateing one of the cards. So to Kerboros' dismay he finds out that Sakura had called upon Windy and scattered the cards all around town. Since Sakura was able to open the book in which the cards were kept she had to have a significant amount of magic. So Kerboros dubs her Card Captor to recapture the run away cards even though Sakura is against it.
Kerboros was nick named Kero-chan because Sakura and Tomoyo didn`t think the name Kerboros fit him. Even though Kero-chan is very cute his real form is much bigger. Kero-chan is a sun beast and rules over the cards Fire and Earth. Because those cards escaped he can`t return to his true form which is that of a golden lion. Since he's stuck as a plush toy he finds it really easy to hide in Sakura's toys . He also at times "dolls out" or becomes very stiff and lifeless like a doll so not to draw attention to himself. And in addition Kero-chan hosts his own show at the end of each episode known as "Leave it to Kero" (Kero ni Omakase). He talks about things that happened in the that episode. Mostly he talks about the costumes that Tomoyo creats for Sakura. But on other occasions he does talk about other things such as Sakura's house.