Pan-soo, a successful businessman in his 40s, is hit on the ground by a person falling from a building. Waking up, he finds himself in another body. Now Pan-soo has to be Dong-hyun, a high school student who gets bullied frequently. He finds out Dong-hyun tried to help a girl, Hyun-jung, and fell off the building. When he meets her mother, Mi-sun, he immediately knows that Hyun-jeong is his daughter. To get close to Hyun-jung, Pan-soo takes hard physical training with her.