Servamp

Mahiru Shirota believes simple is best, so he expects nothing unusual when he adopts a stray black cat and names it Kuro. He soon discovers that the cat is actually a lazy vampire representing Sloth, one of seven powerful vampires known as Servamps.

After accidentally forming a contract with Kuro, Mahiru becomes tied to his power and pulled into a conflict involving the Servamps and their siblings. He meets others with similar contracts and learns that each supernatural bond reflects very human desires and weaknesses. The boy who wanted to avoid every troublesome situation finds himself at the center of an enormous one, but begins to understand that walking away when he can help is not the kind of simplicity he truly believes in.