Witness

No one actually witnesses Saitama defeat Vaccine Man in the chapter Witness, since he finishes the monster off before any S Class hero can arrive. King later stumbles onto the corpse while retrieving his dropped handheld game and is mistakenly credited as the one who killed it.

In Witness, Vaccine Man attacks A City and the Hero Association scrambles to send help, but Saitama destroys the monster before any S Class fighter can respond. King then wanders into the aftermath while retrieving his dropped handheld game, Moe Moe Chronicle 2, and is wrongly assumed to be the hero who killed Vaccine Man.

King is mistaken for Vaccine Man's killer because he happens to walk past the monster's remains right after Saitama secretly finishes it off, having only gone there to pick up a dropped copy of his handheld game. Since no one actually saw Saitama land the blow, onlookers assume the person standing near the body must be responsible.

Witness is a nine page bonus chapter released December 4, 2017 as part of Volume 15 of One Punch Man. Viz Media publishes the same chapter under the title Sighting.

The chapter Witness falls between Disaster Level and A Hopeless Swimmer's Counterplan in the One Punch Man chapter order. It is a bonus chapter tied to Volume 15 rather than a numbered mainline chapter.