Mugen Spiral [Manga]

Yayoi, a mystic with a great deal of powers, is attacked by Ura, the thunder-wielding son of the dying Demon King. Using the Cat God Rosary to seal Ura into the body of a cat, Yayoi is able to defeat him. Though he is her enemy, she carries him home with her.
As the story goes on, Ura is able to assume human form if the rosary is removed. Yayoi can also temporarily release him into his true demon form by breaking one of the 54 beads of the rosary, however for him to break the spell, all of the beads must be broken.