Do Seong-mok is a towering, muscular student with a cold, unreadable expression and a quiet, menacing presence. Rarely speaking, he relies on sheer strength and intimidating body language to make his point. With sharp features, short black hair, and a stoic demeanor, he stands out as a silent enforcer within the Union gang. His loyalty is fierce, especially to his partner Dongha Baek, and his calm, controlled nature hides a brutal force that only emerges when absolutely necessary.