I don't think I will watch it again, but I highly recommend it. It's devastating when she said: "Why when they are apoloziging I have to run away?" You can feel her loneliness, the way she don't has no one to turn to, through all movie.
The story is so poorly written... some reactions don't make any sense... I mean, the policeman lets that killer doctor free, even if later he tries to make everyone zombie and kills another character... and that is just one example. Is it enough with "I changed the pills". No, tell everyone why it is better to keep the doctor isolated, but no.
If you want something light and entertaining where the problems are solved magically and no one has consequences for their actions, you can enjoy this, but I doubt it if you want a good story.
I think he provoked the miscarriage of Seyoung with the herbal medicine because he was married, and now he lives with guilt. So, every time he sees his son, he is going to remember what he did.
It's really a beautiful movie. Don't expect a romantic story, it's more about the relationship of the main protagonist with his family, especially with his father.