They both have a thriller feeling and a very dark back story
His daughter was asking for help in a discreet manner yet he was clouded with the insane “salvation”.
Sang mi’s father grief that turns into an obsession cause he thought he couldn’t save his son in this world he could at least save at the other world he thought of that as a second chance to correct his mistakes to hold his world that was falling apart and his son’s death was the last straw he felt that he was the reason for his son's death and his remorse was the thing that led to his end.