It's Kissshot's first servant, who tried to commit suicide by sunlight, only for his ashes to gather at the white-Snake shrine (because apparently, there's an uninterrupted wind current from the south pole to japan) and recover consciousness around the start of the story. He's one of the main reason the whole story happens, and while it has not been stated outright yet, there are hints that Araragi may be related to him in more ways than one.