Siwoo just looks too grown for his age.

I had to remember the definition of "brooding" and it fits Siwoo well. I mean, when was he happy ever?
"When someone is described as brooding, it generally means they are deeply unhappy, preoccupied with morbid thoughts, or exhibiting a somber and threatening mood."

reminded me of the same thing ahaha

I think brooding fits with the whole I'm so mysterious