Female New Identity: Oh Hyejin Dongcheonpa Undercover / Detective (Corporal) at Incheon Metropolitan Police Agency, Narcotics Investigation Unit Team 1 To find her father's killer, she sought out Choi Mujin, the boss of Dongcheonpa—the nation's largest drug syndicate where her father belonged—and joined the organization. She was given a new identity and became an undercover mole within the police force.

Male CEO of Hotel Liber / Boss of Dongcheonpa, the nation's largest drug syndicate He was a fellow gang member and a brother-like friend to Jiwoo's father, Yoon Donghoon. He tells Jiwoo that her father's killer is among the police and helps her seek revenge. From the moment Jiwoo joins as a recruit, he treats her like his own daughter, and Jiwoo looks up to him as an adoptive father figure beyond just being a boss. Unaware that Donghoon was a police mole, he maintained a close friendship until he discovered a wiretap inside a lighter Donghoon gave him as a gift. Following his principle of killing traitors with his own hands, he killed Yoon Donghoon himself.

Male Detective (Sergeant) at Inchang Metropolitan Police Agency, Narcotics Investigation Unit Team 1 He has spent a difficult time blaming himself for his younger sister's death and became a police officer to find the culprit. His first meeting with Yoon Jiwoo was disastrous, as she ruined a six-month planned undercover operation while trying to catch a murderer. When Jiwoo was later transferred to the Narcotics Unit, he threw a fit of disapproval. Though he acts prickly on the surface, he is a tsundere who looks out for her in various ways once they start working together in the field.

Male Team Leader (Captain) of Inchang Metropolitan Police Agency, Narcotics Investigation Unit Team 1 He has been in charge of planned investigations for years to take down Choi Mujin of Dongcheonpa. He knows the secret behind Yoon Donghoon's death.

Male Second-in-command of Dongcheonpa, enforcer, and Choi Mujin's right-hand man He is displeased with Yoon Jiwoo and believes she will become a liability to Choi Mujin and the organization. However, he does not act against her since she is a member protected by the boss. He manages the 'Gym,' where the main members of Dongcheonpa are trained. He is a loyal subordinate who offers unwavering devotion to Choi Mujin in any situation.

Male Former member of Dongcheonpa / Drug dealer He lost to Yoon Jiwoo during training within the organization. Out of spite, he attempted to sexually assault her but failed. As punishment, Choi Mujin slashed his face with a knife and expelled him. He now operates as a drug dealer distributing a new LSD-based drug. While Dongcheonpa's drug production temporarily halted due to internal rebellion, he quickly grew into a powerful competitor.

Male Former member of Dongcheonpa / Drug dealer He was expelled along with Do Gangjae for the attempted sexual assault of Yoon Jiwoo.