On an unnamed Earth-like supercontinent planet, powerful monsters and villains have been wreaking havoc in the cities. To combat them, the millionare Agoni created the Hero Association, which employs superheroes to stop them. The heroes are ranked from Class C to Class S. Saitama, an unassociated hero, hails from the metropolis of City-Z and performs heroic deeds for his own entertainment. He has trained himself to the point where he broke his "limit" and can effortlessly defeat any opponent with a single punch. But he is now bored with his own omnipotence and frustrated because he lacks a challenge. ...more on Wikipedia