Ura

Ura, the son of the current demon king, attacks Yayoi in order to steal her powers of healing so he can save his dying father. Yayoi uses the Cat's God Rosary to seal Ura's true nature and her spell causes him turn him into a black cat when wearing the rosary, and to assume a human form when it is not. Both determined to steal Yayoi's powers and curious about her, Ura continues to remain with her after being sealed, calling her his "prey" and protecting her from other demons after her powers. Though he can be rude and talks crudely, he is kind hearted and deeply concerned with those he loves. He finds it both annoying and alluring that Yayoi can see through his words to understand his true intentions. source: wikipedia