Saitama

Saitama is a bald, unassuming man who trained himself into the strongest being alive, capable of ending any fight with a single punch. He hunts down monsters and villains not for glory but out of habit, going through the motions with a flat, bored expression because nothing has challenged him in years.

The joke is structural: every show promises a hero's journey, and Saitama has already finished his, off-screen, before the story starts. Furukawa's delivery keeps him deadpan through apocalyptic fights and grocery-store errands alike, and that consistency is what makes his quiet longing for a worthy opponent land as funny and, eventually, oddly touching.