Real name Park Junmo. In high school, he was a notorious troublemaker and the top fighter in all of Daejeon, but through his connection with Seok Dohyeong, he avoided straying further and became a police officer. One day, his senior, Detective Seok Dohyeong, asks if he wants to take on a new job in Seoul, proposing an undercover investigation into the Gangnam Union. Though he initially refuses, he accepts after Prosecutor Jo Changsik mentions his father's drug addiction and promises a one-rank special promotion upon success; Junmo counters by asking for a two-rank promotion instead of a reward. Thus, Junmo successfully infiltrates the Gangnam Union by posing as Kwon Seungho, the cousin of Kwon Taeho—a former member and Gicheol's best friend who died a year ago. However, he is thrown into turmoil upon learning that his wife, Euijeong, was Gicheol's senior in the Hakdong Cathedral choir during high school, and that Gicheol is also aware that Euijeong is a police officer.

Originally a DJ at a club in Gangnam, he became a member of the Gangnam Union at the suggestion of the then-boss, Jang Gyeongchul. However, after enduring constant one-sided mistreatment from Jang Gyeongchul, a furious Gicheol leads his crew in a coup, raiding Jang Gyeongchul's residence. Gicheol's crew kills Jang Gyeongchul and all the other executives, though Gicheol's best friend, Kwon Taeho, dies in the process. Gicheol then becomes the new boss of the Gangnam Union. One day, Junmo appears before him, disguised as Taeho's cousin, Kwon Seungho. Gicheol is suspicious at first but eventually accepts him as a member. However, he is shocked to see Junmo with Euijeong by chance; surprisingly, Gicheol already knew Euijeong was a police officer. Flustered, Junmo fails to mention that he and Euijeong are married, instead claiming she was just his senior in the Taekwondo club during elementary school, but Gicheol remains suspicious of him.

Park Junmo's wife. An ace in the Security Division of the Seoul Metropolitan Police Agency.