Saitama is too powerful; so powerful that it eliminates all the fiercest monsters with a simple punch. Discover the story of the most powerful superhero in this manga that will put you K.O.!! Blast, the number 1 of the S class, appeared before Saitama and Flashy Flash! What is the goal of this enigmatic hero looking for a strange cube? On the surface, the fights rage against the lieutenants of the Association of Monsters and the heroes are in trouble. Even Genos is in trouble. His energetic heart gets excited and risks to explode from one moment to the next!