Saitama, a seemingly ordinary man, has a unique hobby: being a hero. After training relentlessly for three years, he became so powerful that he can defeat any opponent with a single punch. However, this overwhelming strength has left him bored, as there are no challengers capable of exciting him. One day, 19-year-old cyborg Genos witnesses Saitama’s power and desires to become his disciple. Together, they join the Hero Association, hoping to gain recognition and contribute to society. Saitama embarks on a new journey, meeting allies and foes, all while searching for the thrill of battle he once had.