A few more questions
Why did Mi-sun‘s father accelerate and switch tracks on the train in 1988? He had the attacker dad down with a punch already. It was just explained as ‘then everything happened so quickly’ in the flashback. What was he trying to accomplish? As he was just a guard did he even know what he was doing?
Who or what was the significance of the little girl ghost they initially saw on the tracks and stopped the train for?
Who was the woman who was repeatedly shown sitting alone on the bench by the train station? I assume she was a ghost?