A defector from North Korea. Because his identity being revealed could endanger those around him, he hides his past and combat abilities, living as an ordinary family man while silently enduring the tyranny of society. He is incredibly patient and gentle, to the point of overlooking insults and unfair treatment at work to prevent his cover from being blown. Having survived the trauma of being a North Korean special forces operative and an NIS black ops agent, he is numb to most physical pain. While he usually avoids conflict, he reveals his hidden true self when his firm moral standards are violated. In that moment, he transforms into a cold, meticulous fixer who shows no mercy to enemies, possessing sharp situational judgment and heavy charisma that refuses to compromise with injustice. He is raising his daughter alone after his wife passed away. He is close friends with Seong Hansu and Park Jincheol. He is Kim Minji's father and speaks with a perfect Seoul accent.

Seong Taehun's father. He possesses a serious and calm personality, never losing his composure. Although he appears blunt and rarely smiles, he harbors deep affection and fierce loyalty for his child and friends. He runs a Taekwondo dojo, where he shows a warm side by setting aside his strictness to guide children kindly at their eye level. When his son gets into trouble, he takes responsibility first for failing to teach the true meaning of martial arts, disciplining him with merciless kicks to make him realize the weight of violence. While showing desperate paternal love for his child, he also enjoys playful humor when hanging out with his colleagues.

Park Dabin's father. A Brigadier General in the Marine Corps and a member of a private military company, he possesses incredible durability and overwhelming strength. Usually, he has a recklessly bright and cheerful personality, always grinning and acting sly. However, if his loved ones or family are in danger, his eyes change instantly, revealing a terrifying murderous intent and ferocity. He is an extreme 'daughter-fool' whose love for Park Dabin transcends imagination. He becomes an infinitely weak and tender father in front of his child, but shows reliable loyalty and playfulness with his friends. He is deathly afraid of his wife. He knows Manager Kim is from North Korea but keeps it a secret. He is close friends with Manager Kim and Seong Hansu.

Manager Kim's daughter and a student at Songin High School. Having grown up under her father after her mother passed away early, she bickers with him often but relies on and loves him deeply in her heart. She has a very strong-willed and proud personality, unable to stand by injustice. Even when facing school violence, she has a strong side that stands up boldly without losing heart. Although she is kind and quiet at school, Joo Hyeri keeps picking on her. Using the Taekwondo her father taught her as a base, she is a spunky girl who knows how to protect herself when necessary. She has no idea her father is from North Korea or that he is a master fighter; she believes he is just an ordinary office worker. 18 years old.

Seong Hansu's son. A Taekwondo genius high schooler whose specialty is sharp and flashy kicks, capable of perfectly suppressing opponents without blinking an eye even in an 18-on-1 fight. Rather than dark violence, he has a rough adolescent temperament but also a cute charm. He has the boldness to constantly talk back to his blunt father due to his inherent troublemaker streak. He occasionally causes major trouble, such as being caught by the Yoojung police station after fighting with other groups. Even after being severely disciplined by his father in the middle of the empty dojo and rolling on the floor, he never loses his spirit. He has a cheerful and fearless personality. While he has a warm side, hanging out naturally like a neighborhood older brother with the young kids at his father's 'White Taekwondo' dojo, he also possesses uncontrollable playfulness and a persistent competitive streak when with his friends.

Park Jincheol's daughter. She is smart and spunky, with a basically very bright, cheerful, and playful personality typical of a teenage girl. However, in front of her overprotective father, she is a realistic daughter who constantly nags and snaps at him. No matter how much she scolds her dad, she relies on and loves him more than anyone. Having grown up receiving plenty of love within the family, she is warm to those around her. She believes her father is just an ordinary soldier. 18 years old, Gangdong High School.

A very despicable and cold-blooded character who will use any means necessary to achieve his goals. He is cruel to his enemies without a drop of blood or tears, and possesses immense madness and obsession to maintain his power. However, in front of his only daughter, he is more tender and devoted than anyone else.

She looks elegant but is insolent and has a very strong sense of possession. She is prickly about everything and treats people arrogantly, looking down on them. Raised under her father's overprotection, she has a bold and toxic temperament, needing to get whatever she wants. She bullies Kim Minji because her crush is nice to Minji. She has many friends. 18 years old, Songin High School.