They are teasing Seo Yul's death so much in the dialogue and the previews that I think it's a deliberate misdirection.What…
Yul should not try to do things himself and keep his illness a secret. It's like he has no hope, just waiting to die. I bet Buyeon can take the blood parasite out since it's a relic from Jinyowon. I also think he will not die.
I'm somewhat satisfied with the ending though I wish there were more sweet scenes. They even cut short of the last kiss. In the end, they worked together to make the world a better place. They make a good partnership and respect each other's ideas and decisions. They are fun to watch up till the end.
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