Jinx

Baek Junmin

A fighter fighting against Joo Jaekyung. While shaking hands before the fight, Junmin tells Jaekyung, "Don't you remember me?" hinting that Junmin is connected to Jaekyung's past.

Choi Heesung

An actor of the same age as Jaekyung,[4] Hyusung also works at the same agency. Hyusung takes a nap with the script of Extreme Worlds on his face and learns that Jaekyung is ready to meet him. To prepare for an important scene, Hyusung signs up for personal training and kickboxing with Jaekyung, who films it for his blog. Before leaving, Hyusung also takes a selfie with Jaekyung to take with him on the road, as he says people like pictures of them together. He is attracted to pretty faces like Dan's and stalks him, much to Jaekyung's displeasure.

Randy Booger

A fighter who fights Jaekyung at light heavyweight. Booker is introduced as the main event contender for MFC 272, known by the nickname "The Butcher". Like Jaekyung, he has just weighed in and is facing him for the first time. After spitting in Jaekyung's face, Randy provokes him into punching him and asks if he is scared.

Hwang Yoon Gu

Jungwoo, the youngest member of the team at 20[3][2], does not like being called a "potato". At a drinking party, Jungwoo falls asleep at the table. While watching a video of Randy, he becomes angry at him for making fun of the others. Jungwoo questions who he thinks he is and states that Jaekyung will tear him apart. Confused about why he is so close to Dan, he wants to train with Jaekyung. Although he is a little jealous, he does not take it out on Dan. In fact, Jungwoo is delighted and thanks Dan for arranging for him to spar with Jaekyung.

Kwak Junbum

A former athlete who practiced judo, Junbum is said to look much older than his age at 21. Like the other members, he participates in team activities such as gym training and social events. He is a member of Team Black.

Kim Changmin

An athlete from Team Black and a national player. He says he is the second most handsome member of the team after Jaekyung.

Chon Yosep

He is a trainer in his own right and the oldest athlete in the Black Team at 37 years old.[2] He is Jaekyun's sparring partner and a former national champion. Yosep is one of the few people who is not afraid of Jaekyun when he is angry, earning the hot-tempered boxer's respect for him. He notices that Jaekyun usually does not go to parties with the others. During Jaekyun's fight with Randy, he tries to motivate the former, but to no avail. He brings fried chicken to the team along with Namwuk.

Oh, Daehyun

An energetic and friendly athlete from Team Black. When he comes to Dan's welcome party, he cheers him on and jokes that the other athletes will eat his portion if he doesn't. Upon hearing that Jaekyung didn't show up for the party, Daehyun counters that Jaekyung went to see his physical therapist. When Jaekyung invites Dan to join him at the arena, Daehyun worries about Dan and asks him not to go. When Dan agrees to go on stage, Daehyun acts as the MC and announces Dan's entrance.

Shin Okja

Dan's grandmother is currently sick and is in the hospital receiving treatment. She is happy to see Dan and says that he shouldn't have come because she knows how busy he is. She is happy in his presence and says that she never misses a meal and then asks about Dan. She asks the nurse to bring her some yogurt drinks for Dan's arrival. When she learns that Jaekyung has visited her, she is delighted and effusive in her praise.

Pak Namwuk

At 38 years old, Namwook is Jaekyung's manager and trainer for Team Black. He arranged for Dan to meet Jaekyung as his new physical therapist, and told Dan that everything would be fine as long as he did not irritate Jaekyung. He was ecstatic about Jaekyung's victory in the arena and treated Dan well, so he introduced him to the other fighters at the gym as Jaekyung's personal trainer. He is the one who encourages Dan, calling him Doc so that others will treat him with even more respect. After noticing Jaekyung's improved behavior, Namwook praises Dan, holding him responsible for it. Namwook is married, his wife is also an athlete. They have two daughters and a son.

Ju Jae Kyung

By the age of 26, boxer Ju Jaekyung has become an undefeated legend in the mixed martial arts championship. Feared and respected for his dominance in the ring, Jaekyung is known as a tyrant, and here's why. Jaekyung confided in Dan that he has "bad luck" where he loses fights unless he spends the night with someone first. Repeatedly calling him to get him to sign a contract to become his personal therapist on paper, Jaekyung sees Dan as a way to continue winning in the fighting ring. Despite Jaekyung's ferocity during fights and harsh words, he is able to understand what is best for Dan. Over time, Jaekyung begins to enjoy being around Dan and becomes more outgoing with the other members of his gym.