A muscular southpaw boxer with short hair, a sharp gaze, right cheek scar he is a disciplined former Marine 1,20th class who originally entered the dark loan shark underworld to clear his mother's predatory debts. Rising from a debt collector's target to a legitimate World Boxing Champion, he serves as the primary protagonist, forced out of the professional arena to smash Im Baek-jeong's brutal, illegal dark-web IKFC fighting ring. He is very kind, kind hearted, gentle. But fierce when needed.

A lean, tall boxer with an athletic frame and a hand injury. This street-smart, humorous former Marine 1,216th class, braved the underworld to help destroy Smile Capital. After retiring from fighting due to his injury, he became Gun-woo’s dedicated coach and corner supporter. He acts as the secondary protagonist and tactical anchor, ultimately forced back into action when the brutal IKFC dark-web fighting league targets his chosen family. He is funny, charming, strong, very smart. Kind too.

A warm, middle-aged woman with a gentle appearance, soft features and a caring, motherly presence. She is Gun-woo’s devoted mother and runs a small modern café, living together with Gun-woo and Woo-jin while supporting her son’s boxing career. After Gun-woo returns to professional boxing, So-yeon becomes increasingly worried about his safety, fears that he will once again be dragged into dangerous situations. She serves as Gun-woo’s emotional anchor and one of the main people the others are determined to protect when Baek-jeong targets her to reach Gun-woo. Kind, affectionate and humble, she is deeply protective of her son, easily worried when he is in danger, but remains caring and resilient even when threatened.

Tall, polished and sharply dressed, with neat dark hair and a refined, wealthy appearance. He is a powerful third-generation chaebol and eldest son of Il Corporation’s chairman, with influential family connections. In Season 2, he uses his wealth and connections to help Gun-woo and Woo-jin fight Baek-jeong’s organization, eventually creating a plan for their final confrontation. Confident, intelligent and resourceful, he is more determined and responsible while remaining composed under pressure.

A sharp, intense former Marine 1st CLASS typically seen riding a motorcycle in a rugged black leather jacket. Previously legendary, elite knife enforcer under President Choi, his background involves a dark deal with Smile Capital to save his pregnant family, carrying massive guilt over his peers' deaths. Shockingly revealed to be alive in Season 2, he acts as a protective mentor and backup fighter. He takes on a heroic guardian role, helping Gun-woo and Woo-jin smash the underground ring.

A rugged, street-hardened fighter with a fierce look and intense military discipline. As a former Marine 703th enlistment class turned loan shark, his background mixes tactical marine grit with underworld survival skills. Originally a crucial ally who connected the duo to safe money in, he returns alongside corporate heir Min-beom to assist Gun-woo and Woo-jin. He acts as a resilient supporting fighter, stepping in to fiercely take on IKFC goons despite sustaining severe injuries.

A monstrously bulked-up fighter with tight, slicked-back hair, a defined jawline, and a menacing, sharp gaze. A former professional boxer whose career ended in deep disgrace after a violent incident, his background is rooted in brutal, pure evil. He serves as the primary antagonist, running the brutal, dark-web based IKFC illegal gambling and boxing league, driven by coercion to drag top fighters like Gun-woo into his underworld ring. He is very ruthless and merciless.

A sharp-looking strategist wearing casual street jackets. Under his real identity, Lee Dong-hyeon, his background is rooted in elite espionage as a former National Intelligence Service (NIS) black ops agent. He acts as the brilliant operation planner, briber, and decision-maker for Im Baek-jeong's IKFC syndicate. He serves as a critical supporting antagonist who weaponizes his chatroom to orchestrate tactical prison breaks and ground the impulsive CEO.

A highly stylish youth with distinct, vibrant green hair. Emerging from the tech-savvy underground criminal circuit, his digital expertise makes him an invaluable operational asset. In Season 2, he serves as the elite, lead hacker who controls and maintains the dark-web broadcasting systems for Im Baek-jeong's illegal IKFC fighting ring. He acts as a key technical antagonist, protecting the organization's online footprint from law enforcement.

The tragic, highly dangerous right-hand man to villain Im Baek-jeong. A dishonorably discharged Special Forces sergeant and explosives expert, he joins the brutal underground fighting circuit to fund medical treatment for his cancer-stricken wife. He utilizes a lethal, rational MMA combat style against the heroes. Driven by love rather than pure greed, he ultimately betrays his boss to the police, leading to his tragic execution. He is a former Sergeant in the 17th Special Forces