Life becomes quite boring when you can defeat any opponent with a single punch. Nothing about Saitama resembles a superhero – from his expressionless face to his bald head and average physique.

However, this seemingly ordinary man has an unusual problem: he cannot find an opponent strong enough to challenge him!

The Monster Association's big heads are exterminating the S-class heroes one by one... until the strongest man in the world, King, takes on the crisis. Although the monsters boil with hatred, King remains calm and unshaken. But can his calmness prevent disaster?