I'm not 100% sure about this cause i didn't translate everything, but I think he's actually already dead. I believe his soul was tied to the forest, and he essentially couldn't pass to the afterlife unless he takes a soul with him. He became sort of an evil spirit. I think he was planning to take geonpil's soul at first, but then they ended up reconciling and then oghyung was able to pass taking along the soul of an elderly woman, I actually can't remember if that granny had any relevance in the story before this event.

This is already completed (27 chapters), he ends up with the ghost.
https://boylove.cc/home/book/index/id/31829