So I have a theory that the demon king Derkila went to the human world to live there cuz he was bored or smt and like in the human world he encountered kid iruma and then kid iruma helped him or saved him, then as a reward Derkila put his crest on iruma for sullivan to find to make him like the new demon king type shi, then like fast foward when iruma is like 14 that's when he was taken by the netherworld to start his path
So I have a theory that the demon king Derkila went to the human world to live there cuz he was bored or smt and like in the human world he encountered kid iruma and then kid iruma helped him or saved him, then as a reward Derkila put his crest on iruma for sullivan to find to make him like the new demon king type shi, then like fast foward when iruma is like 14 that's when he was taken by the netherworld to start his path