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! 
In an underground labyrinth, Puri-Puri Prisoner encounters Garo, who is now stronger than ever! Meanwhile, Saitama teams up with the hero Flash while both are lost underground. On the surface, Nyaan toys with Class-A heroes until Drive Knight appears!