Saitama is a hero who has become so powerful that he can defeat almost any opponent with a single punch. After years of intense training, however, his overwhelming strength has taken away all excitement from battle. Searching for an enemy capable of giving him a real challenge, he continues his heroic activities almost out of boredom and eventually joins the Hero Association alongside Genos, a cyborg who becomes his disciple. Between gigantic monsters, extraterrestrial threats, and rival heroes, Saitama faces increasingly absurd dangers while desperately trying to recover the thrill that once inspired him to become a hero.