Witness (目撃, Mokugeki) is an extra chapter included with Volume 15.
Summary[]
Vaccine Man attacks A-City as the Hero Association's staff rush to get in contact with as many heroes as possible. Saitama kills the monster before any S-Class heroes arrived. Shortly afterwards King stumbles onto Vaccine Man's corpse when picking up his video game, Moe Moe Chronicle 2 from the floor, and is mistaken as the monster's killer.