Maybe this girl save Nakyum...

How? It is not like she can just say - “Hi, I know him (I am his noona, sister (or whatever), let him leave with me” and Seungho would be ok with it. He would probably kill her. What can this girl DO exactly? Also, she is not his sister, Nakyum is an orphan.

When will Seungo’s kinder, saner, brother make another appearance? He appeared then disappeared so quickly.

I don't think she is useless