Saitama has started his passion for being a hero for fun. Later, he became invincible after three years of hard training. He is now unbeatable and defeats the opponents in one punch. Saitama keeps working as an official hero in the Hero Association, along with his loyal student Genos.
One day, monsters of the Monster Association come to kidnap the child of one of the Hero Association’s leaders. The S-class heroes make a plan to raid on monsters’ place for the release of hostages. While a Human Monster, Garou was arrested during a fight and woke up inside the Monster Association space.
