Kim Dan, a struggling physical therapist, has always found himself caught in a web of bad luck. Between caring for his sick grandmother, dealing with relentless loan sharks, and being blacklisted by a former boss, his options are running out fast. So when he’s unexpectedly hired to treat Joo Jaekyung, a high-paid MMA fighter, it feels like a stroke of luck. But things take a surprising turn when Joo calls him the night before an important match with an offer he can’t resist: $5,000 for a special treatment.
Joo claims he has a “jinx” that needs fixing, but it’s not the kind of treatment Dan is used to. Joo may be a savage in the ring, but he’s even more intense behind closed doors—and Dan isn’t sure he can handle the heat. Still, desperate for money, Dan agrees to the risky proposition. Could this one night change everything for him?
At 29, struggling with debt and personal hardships, Kim Dan takes a risky job as Joo Jaekyung’s personal therapist, unaware of the boxer’s volatile nature.
At 26, undefeated MMA champion Joo Jaekyung hires Kim Dan as his personal therapist, believing Dan is the key to breaking his "jinx," while slowly growing closer and more personable over time.
At 20, Yoongu, the youngest team member, dislikes being called "potato" and, after a night of drinking, angrily defends Jaekyung against Randy's taunts, later thanking Dan for arranging a sparring match with the champion.
Heesung, an actor and Jaekyung’s age, works at the same talent agency and, after training with Jaekyung for an action scene, films their kick-boxing session for his vlog, later pursuing Dan—much to Jaekyung’s irritation—thanks to his attraction to Dan’s looks.
Currently ill in the hospital, she’s happy to see Dan and insists he shouldn’t have come, but cheerfully shares that she never skips meals and even asked for yogurt drinks for him; she’s thrilled when Jaekyung arrives and showers him with praise.
At 38, Namwook is Jaekyung's manager and Team Black's coach. He arranges for Dan to be Jaekyung's personal therapist, advising him to avoid irritating Jaekyung. Proud of Jaekyung’s success and kind to Dan, he introduces him to the gym and encourages the nickname "Doc" for respect. Noticing Jaekyung’s improved demeanor, he praises Dan for his influence. Married with three children, Namwook’s wife is also an athlete.