Responses
There is a chance that it was too late for the kid to sever his connection to the demon king. Perhaps it's a type of curse that is intertwined with the soul, and purification would do more harm than good. I guess one way to find out is by reading the novel since details like this are usually cut out when converted to another medium.
Ch. 31 - if that's a kid being controlled by a demon who JUST had his first kill UNDER CONTROL shouldn't he be purified and converted, given a chance to repent?
I get that he was bad (bully) but he was also a kid. To just KILL him…
(and before yall come @ me, the bullying I went through included them trying to kill me thrice and I still don't think they should be dead much less burnt alive to ashes. Tbh, I don't even think they should be punished now, if they've changed and become normal people, because we truly were just kids, the adults should've done something to stop them and protect me, not expecting they would magically change that instantly.)