yuseong is yoojin's twin brother, sometimes he is very childish, but plot twist he is strong, he is able to fight many people, because,Yoojin said he is obsessed with becoming a strong man

he always wears a hat and he also has the nickname "cap guy" people always think yuseong is weak, but when they see him fight, people are even shocked

sometimes he also protects Yoojin wherever Yoojin is, because Yoojin can't fight compared to his twin brother