Ga-in, a high school student, witnesses the deaths of her relatives who die from a curse. Once she finds out that she is the next target, she asks her boyfriend to help her break the spell.

On the first day of school, Sin-woo hears about the dangerous student council who even the teachers avoid. When he saves a kid from being cheated by them, he becomes known as 'one punch man.' After being expelled from defending a friend from the student council's torment, he is invited to join them, which confuses him.