Blood collar (Jigoku shoujo fanfic)

Because of what he did Ren is no longer favoured by Ai , she stays away from him, leaving him out of every mission. His orders remain the same- look after the girl that unexpectedly joined their team. Of course this girl isnt a normal human, just as Ren isn't one. She had made a contract with Ai to work for her for a hundred years if Ai provides her with human body.
Despite looking like a human she does not know how to behave, walks on all fours and talks only telepatically.
But maybe she could be just the right thing to mend Ren's broken heart...