After watching episode 12 I'm pretty sure that the main lead's FATHER is the culprit.

In this episode, we find out the female lead's nightmare. Her parents will lead a very happy life, but she can't find the male lead. Looks like the main lead will be disappeared. That happens if the male lead was died or he was never born. If the main lead's father is the culprit, then he will be arrested . This is how the main lead will never born. Besides this logic I found a wierd fillngs about his father. He looks very suspicious.

If this happens then it will be a Sad ending.??

I know my English is not so good, but I think it's quite understable.