Na Hwa-jin

He sports slightly unkempt, dark black hair. While he usually lets it fall naturally around his face or casually ties it back, it occasionally appears in a wavy, slightly longer style.His gaze is intense, sharp, and focused, often carrying a somber and serious demeanor usually keeps a faint, trimmed stubble.Hwa-jin boasts a tall, lean, yet heavily muscular and athletic build, honed from his past as a military captain in the Special Mission Battalion.He is defined by a monochromatic, all-black wardrobe. He is frequently seen in tailored black suits, which symbolize the loneliness and sorrow tied to his fiancée's tragic death.When working off the clock, his style shifts to simple black t-shirts and dark, solid jeans.

He adopts a "ruthless" approach to discipline. He firmly believes in accountability and refuses to coddle disruptive students, abusive parents, or unethical teachers.Relying on his elite military and martial arts background (Krav Maga), he analyzes problems logically and strikes with chilling precision rather than pure, blind rage.Despite the dark and heavy subject matter, his interactions with his team at the Educational Rights Protection Bureau (ERPB) and the troublemakers he reforms feature moments of wry, deadpan humor.

The ERPB stands for the Educational Rights Protection Bureau, a government agency. It acts as a specialized task force authorized to use unconventional, often physical intervention to restore order, protect teachers, and stop school violence.The bureau tackles systemic school issues that traditional teachers and administration cannot handle on their own. The bureau travels from school to school to aggressively combat issues like organized gang recruitment, extreme bullying, corruption, substance abuse, and teacher extortion. sparked actual real-world debate in South Korea. Several regional education superintendents have proposed establishing similar, real-life agencies to protect teachers from burnout and parent harassment.

Na Hwa-jin: A former Special Forces captain who acts as the lead inspector for the bureau. He is the show's primary action hero, bringing ruthless, unconventional, and highly physical methods to put out-of-control students and corrupt adults in their place.

Choi Gang-seok: The powerful founder of the ERPB and a government minister. He reunites with Na Hwa-jin to restore peace to the school system using strict, unflinching authority.

Im Han-rim: A dedicated and sharp inspector within the bureau. She works alongside Na Hwa-jin to investigate intense cases of school violence and protect vulnerable victims.

Bong Geun-dae: A devoted deputy manager and key investigator on the ERPB team who helps track down bullies and hold corrupt parties accountable.