Dog

When he first appears in the anime, he is silent and distant. However, as the story progresses and Saya starts to recover more of her memory, he starts to talk to her. He tells her that his mission is to fulfill someone's wish. That involves helping her regain her memories and "waking her up." When Saya asks who's wish it was, he says that information cannot be released as it would violate the contract. In the last episode of Blood C, it is assumed that Saya's past-self, before Fumihito drugged her, was the one that had made the wish.