In a chaotic world plagued by monstrous threats, superheroes are ranked and regulated by the Hero Association, battling everything from mutated beasts to alien invaders. Among them, a mysterious and unassuming man named Saitama lives in obscurity in City Z. Bald, emotionless, and dressed in a yellow jumpsuit, he’s unlike any other hero — because he can defeat any enemy with a single punch. Once an average office worker, Saitama trained obsessively for three years, gaining immeasurable power. But his overwhelming strength has left him bored and detached — craving a real challenge that never comes. When the city is attacked by a string of unusually coordinated monsters, Saitama steps in, saving countless lives, but gets little recognition. He soon meets Genos, a fiery young cyborg driven by vengeance. Impressed by Saitama’s power, Genos becomes his disciple. Together, they join the Hero Association, encountering eccentric and powerful heroes like the psychic Tatsumaki, martial arts master Bang, and the vain superstar Amai Mask. As a new threat emerges — a powerful villain known as Lord Boros, who claims to be the strongest being in the universe — the world’s top-ranked heroes are defeated one by one. When Boros arrives to destroy Earth, it’s up to Saitama to face an opponent who might finally push him beyond a single punch.