Though he’s been doing the hero gig for three years, Saitama realizes that the public knows nothing about him. Determined to get a little recognition, he decides to become a pro hero, but first he must pass the Hero Association tests and become a full-fledged member.

Saitama tags along to an emergency meeting of Class S heroes and discovers that a seer has foretold a serious danger threatening the Earth. Though the crisis could occur anytime in the next six months, the heroes are surprised to hear the roar of explosions that very hour!