Cain's valet. Riff dresses Cain and ties his shoes for him, which Yuki considers "a form of communication between the two of them because they've been together so long that they're almost like father and child."
Secretly a high-ranking member of Delilah, he is placed with Cain so that Cain form a close bond with him and be further hurt when Riff reveals that he had always despised him. Riff had murdered his own family and died in the ensuing fire he intentionally set. Resurrected by Delilah and given an alternate, kinder personality, he is the longest surviving of all the dolls, occasionally brought to the organization's hideout and given blood transfusions to keep him alive. However, his will to rebel against Delilah grew stronger as the hypnosis faded, which allows him to kill his original, cruel personality.(Source: Wikipedia)