As the reincarnation of Soloman and the one who will choose the next interim ruler of hell, Dantalion vows to protect William Twining (while hoping he chooses him as ruler). From Makai Ouji: Devils and Realist.
Kurogane helped Fai to live. In-fact, Kurogane offered himself to be Fai's blood source when Fai's vampire blood awakened, making Fai dependent only in sucking blood to survive. In another OVA, Kurogane even cut off his left arm in order to save the other, avoiding Fai from being trapped in a dimension.
