Kero-chan is not your run of the mill guardian. A trend in anime when it comes to guardians, is a power wielding, parent-like figure, who makes the silly unwanting child accept responsibility. Although Kero-chan helps Sakura accept this great responsibility, it is not by force, and repremanding. He and Sakura have their little quirks, and arguments, and they really don't show much emotion towards eachother. There are the favors of cooking hotcakes, and okonomyaki (with noodles), but other than that, they live and work together as roomates. However, their relationship is best shown in episode 15, when they have a big fight. Kero-chan leaves, and Sakura figures he'll come back within the night. Even though she left her window open, he never came back. Sakura begins to grow worried about his whereabouts, and sets out with Tomoyo to look for him. They even attempt to make Lost posters.. ^^;; It just shows you how we take eachother for granted, and that they really never noticed the importance of eachother, untill they were seperated. When he reutrns, Sakura fiixes him his own special room in one of her drawers. ^^
Kero-chan is very important to Sakura and vice versa. Without Sakura, Kero-chan would still be sleeping in the Clow, and would have never met Sakura. Without Kero-chan Sakura would be cluless as to how to catch the clow cards. If Sakura fails to pass Judge Yue's test, all the clow cards will go back, and Sakura will lose all memory of being a card captor. I think this worries Kero-chan somewhat, because he wouldn't want to have never met Sakura. She has housed him, took care of him, and provided him her friendship. If Sakura fails, he would lose that. Therefore he is very serious when it comes to collecting the cards. Not only does he want to save the world from disaster and chaos, he also wants to preserve his and Sakura's friendship. Kero-chan is constantly at Sakura's side, offering advice and encouragement, and becomes extremely defensive when people speak ill of Sakura's card captoring skills.