A group of battlesuit-clad terrorists called "The Paradisers" appears in City F, led by an enormous man known as Hammerhead. Calling for the redistribution of wealth, the group targets the fat-cat Zeniru, who in turn dispatches his bodyguard to defeat them. Unfortunately, Saitama is on the same errand.

Though he's been doing the hero gig for three years, Saitama realizes that the public knows nothing about him. Determined to get a little recognition, he decides to become a pro hero, but first he must pass the Hero Association tests and become a full-fledged member.

A pack of monsters calling themselves the "Clan of the Seafolk" arrive on the shores of City J intent on invading the land. When the hero sent to fight them is defeated easily by the Deep Sea King himself, Saitama and Genos head for the city to help.

The inconceivably powerful Lord Boros has traveled untold distances in search of someone who can cure his boredom: Saitama! With the fate of humanity in the balance, will the two champions at last find in each other the worthy opponent they've been searching for?

The heroes plan the rescue of a child kidnapped by monsters; Fubuki invites Saitama to join forces; Garou awakens deep underground.

After joining the Monster Association, Garou dines and dashes from a restaurant. Saitama, happening to be nearby, pursues him.