I really can't understand the ending can someone explain

That make as two. I think the shaman wanted really bad to be with the late king. Soooo he summoned him. But him being a demon, make the other guy die. So they will be together now, one as a demon and the other as a spirit. I guess. I hope it's like that.

A bit late but here's what I think
https://www.mangago.zone/home/mangatopic/15269050/