Hmmm. The prevailing theory is that the man is not just an abuser but also a murderer, and that he killed each of the women--other than Minnie's character--in the past. Thus, each of the victims is shown where they were killed (pretty obvious with the drowning victim), and also shown with flower imagery, symbolizing their death. When the victims are shown with Minnie, they are ghosts. Minnie avoids becoming the next victim and kills the murderer, avenging the victims. At the end, the ghosts are shown finally at peace, having been avenged, and then 'move on' (disappear). It seems a lot like many fantasy k-dramas, where an aggrieved ghost cannot move on until its grudge is satisfied.
