Cha Woo-Sol ( Kim Min-Suk) was bullied by Bae Seok-Chan (Jung Won-Chang) during his middle school days. He finally felt a sense of relief when he enrolled at a different high school from Bae Seok-Chan, but Bae Seok-Chan transfers to the same high school that Cha Woo-Sol attends. Cha Woo-Sol is unable to take the bullying anymore and he attacks Bae Seok-Chan with a knife. Afterwards, Cha Woo-Sol is sentenced to 3 years in juvenile prison for the attack. Meanwhile, Bae Seok-Chan has to give up boxing because of his injuries from the knife attack.
He wants to get revenge and waits for Cha Woo-Sol’s release from juvenile prison. At the juvenile prison, Cha Woo-Sol meets Jung Do-Hyun (Wi Ha-Joon), who is a former MMA champion. He is in prison for killing three people who killed his family. To survive in prison and whenever he meets Bae Seok-Chan again, Cha Woo-Sol asks Jung Do-Hyun to teach him how to fight.