One on One: Do-yeong is unemployed after graduating college of physical education but gets a job as a trainer in the gym. There, he meets Se-hee, a beautiful and famous sports caster who lives in his neighborhood. He tries to buy her attention but fails several times. Meanwhile, Do-yeong finds out that the gym is planning a way to use Se-hee and he sets out to save her. What is going on during the 1:1 sessions at the gym and what is the plot behind it?