Reality Punch (現実パンチ, Genjitsu Panchi) is an extra chapter included with Volume 19.
Summary[]
Saitama is walking in Z-City reading a manga, thinking about the hero's journey, finishing moves, and hypothetical monsters. While wandering, Saitama encounters The Three Tempest Brothers. The monsters are annoyed by Saitama's obliviousness to their presence, but after Saitama easily kills one of them, the other 2 run back home.