I think one of the things that annoyed me about Sun Woo was that he came across as dull. He seemed like a 2D character…
I also didn't connect with him because from the beggining the series never trully focused on him and Dam if you think about it. I actually felt bad for him cause I feel like he was being used while he was tied with that red thread. I believe he had a slightly character development but we hadn't the chance to see it cause he was presented more of an obstacle for the relationship rather than a human. Because of that I didn't got second lead syndrome for the first time and was able to empathize with Dam more. He had potentional but wasn't portraited well.