Life gets pretty boring when you can beat the snot out of any villain with just one punch.
Nothing about Saitama passes the eyeball test when it comes to superheroes, from his lifeless expression to his bald head to his unimpressive physique. However, this average-looking guy has a not-so-average problem--he just can't seem to find an opponent strong enough to take on!
Hero hunter Gato intensifies his onslaught, so of course Saitama decides now is the perfect time to join a combat tournament. Meanwhile, Class-S hero Metal Bat takes an assignment guarding a Hero Association executive and his son, and before long trouble appears!