The Terrifying City

While Saitama sprawls out with a comic, Genos quietly documents his supposed master's every idle habit, hoping to decode his training. Saitama, worn out by the effort of faking mentorship, learns from Genos that the association eventually removes any C-Class hero who logs no activity for over a week. Already six days idle, he bolts out on patrol before the deadline can end his registration, and he waves Genos off with a made-up lesson about cultivating patience.

Two uneventful days later, on his final chance to stay listed, Saitama is confronted by Speed-o'-Sound Sonic, who wants their rivalry settled. Saitama ignores him, then snaps the ninja's blade in two with his teeth. Rattled, Sonic scatters exploding shuriken across a crowd that Tanktop Tiger had been working for attention, triggering panic. Saitama, still desperate for hero work, takes the excuse and flattens Sonic in an instant. Elsewhere, near Saitama's rundown old district in Z-City, something menacing begins prowling the near-empty streets. Furious at being left on the bench, Tatsumaki complains about the dispatch team already assigning Golden Ball and Spring Mustachio to the area.

The two heroes comb Z-City chasing whispers of a dangerous creature, only to be overwhelmed by Kombu Infinity, who swats their attacks aside and beats them with ease. Disappointed by how weak they proved, Kombu resolves to manufacture the very legend that drew him there. Saitama, returning from a supermarket sale, catches the monster's eye and is attacked. By the time Genos comes home, Saitama is calmly simmering a pot of kombu soup.

Saitama discovers the association's rule that inactive C-Class heroes are struck from the registry, forcing him back onto patrol. He knocks out Speed-o'-Sound Sonic after the ninja's attack throws the crowd into chaos. In Z-City, Kombu Infinity defeats Golden Ball and Spring Mustachio, then targets Saitama, who deals with the creature and is later shown cooking kombu soup at home.

The episode adapts material from chapters 18 through 20 and spans both the National Superhero Registry Arc and the Rumored Monster Arc. Fubuki delivers the closing monologue over the end credits. Several scenes were added or altered for the anime, including the Tatsumaki dispatch-office exchange and the Blizzard Group appearance, both original to the adaptation, along with changes to how Saitama stops a runaway car and how far he sends Sonic to the ground.