Saitama is a hero who only became a hero for fun. After three years of “special” training, though, he’s become so strong that he’s practically invincible. In fact, he’s too strong—even his mightiest opponents are taken out with a single punch, and it turns out that being devastatingly powerful is actually kind of a bore. With his passion for being a hero lost along with his hair, yet still faced with new enemies every day, how much longer can he keep it going?
Ria says "An awesome anime."
With many superhero shows, both animated and live action, the whole story is built off of the hero's back story. One Punch Man challenges this this comically. With every villain and monster sharing their history and feelings (who they are, why they do what they do) as a monologue at their early opportunity, whilst we never really know much about Saitama the superhero besides the fact that he only does what he does because he's looking for a challenge. It's his hobby. He doesn't care about saving the world, he just wants to be good at his hobby and is bored because he has yet to be challenged. Amazing art style.