Onan Earth-like super-continent planet, strange monsters and supervillains have been mysteriously appearing and causing disasters. Tocombat them, the world's superheroes have risen to fight them. Saitama is one such superhero, hailing from the metropolis of City Z and easily defeating monsters and villains with a single punch. However, he has become bored with his power and only gets truly excited when fighting strong opponents that can challenge him. Over the course of the series, Saitama encounters various superheroes, supervillains, and monsters. He gains a disciple in the form of the cyborg Genos and eventually joins the Hero Association in order to gain official recognition. Despite defeating many strong monsters that even the Heroes Association’s top members are unable to defeat, Saitama often gives the credit to S-Class superhero King who is actually an ordinary human.