Sorry, Seong-gu, you didn't pass the vibe check to join Jiyong's crew. You have to be at least as deranged as Choe Miryeo.
I'll be surprised if this is the last we see from him, though. The author wasted a lot of characterisation on him if it turns out it was just for an introductory arc.
Glad to see Gang-ok is dancing to his own mental music as always.