so uh here is what I think, either Mario is Yoon ohs dad or just someone who loved his mother but yeah the former works better. The whole point of resentment and grief, but what if a ghost stays back for love? it is not hard feelings just love they want to be the person they love, so why must a ghost become evil then? Another theory, the show is called peach of time, what if peach travels back in time? right before Yoon Oh's death, and somehow there is a change in events? I believe the hospital track has something to do with this as well