OH SON DO SON

Lim Sejun, who likes to eat, is fat and has a large physique. He has high self-esteem and a firm personality that doesn't even care about being teased for being fat. He has only one friend, 'Seo Hajin'. She has always been learning Jiujitsu to protect Sejun since childhood. One day, Sejun has trouble with a delinquent in the same class, and Hajin sees it and destroys that delinquent. But one night, Hajin is found severely beaten and suffers from a badly injured knee and more serious psychological trauma. Sejun tries to tell the police, but when the investigation doesn't make much progress, he can't control his anger and goes to find the culprit himself, but he's defeated by the delinquent who learned Jiujitsu and finds nothing. Then he learns Jiujitsu from a man named 'Jason' who saved him. Three months later, Sejun, who learned Jiujitsu and lost weight, finds out that a veiled group is involved, and wants to destroy it. A school action drama depicting individual revenge.

While Sejun Im settles things with his fists, his best friend, Hajin Seo, eats and breathes grappling. Together, they fend off bullies on their school campus, but everything changes after a fight that sets Sejun on a mission to hold those responsible accountable for their crimes. What began as a schoolroom brawl quickly turns into a fight for justice and truth as Sejun hits the streets looking for any leads as to what happened on that fateful day.