Zetsuba was a major character in FTS 0. He was the prophecy courier and trainer of the demigods (except they weren't demigods that's just a plothole). After the demigods completed their training, Zetsuba made them all 14 and erased their memories, so that less plotholes could happen, and so that the demigods could meet, DP and Ukod. Wait, doesn't that mean the demigods are actually older than DP and Ukod? I don't know. Anyway, Zetsuba eventually went home, where he divorced the ugly queen of darkness and found a new apprentice.