Life gets pretty boring when you can beat the snot out of any villain with just one punch. S-class hero Blast suddenly appears before Saitama and Flash in search of a mysterious box! But what is it about the box that has the Hero Association's top hero chasing after it? Meanwhile, several heroes are locked in a fierce battle with Monster Association executives when Genos's power core becomes unstable! S-class hero Blast suddenly appears before Saitama and Flash in search of a mysterious box! But what is it about the box that has the Hero Association's top hero chasing after it? Meanwhile, several heroes are locked in a fierce battle with Monster Association executives when Genos's power core becomes unstable!.