In One-Punch Man, Saitama, a hero with an unremarkable appearance, dedicated three years to intense training to fulfill his childhood dream, a pursuit that cost him all his hair. Now possessing such immense power that he can defeat any enemy with a single punch, he faces an unexpected problem: the lack of challenging battles leaves him feeling bored. His routine is upended when Genos, a 19-year-old cyborg, witnesses Saitama's extraordinary abilities and begs to become his disciple. Genos suggests they register with the Hero Association to gain formal recognition for their deeds. Puzzled by the fact that his identity remains unknown despite his feats, Saitama agrees. As he forges bonds with new allies and confronts fresh threats, Saitama joins the Association in hopes of reigniting the passion for combat he once cherished.

In this installment

After defeating Boros and his army, Saitama goes back to his normal life in Z-City. Yet, monster attacks become more frequent, putting a heavy strain on the Hero Association's resources. To cope, the organization hatches a daring scheme to enlist criminals as temporary allies. At the first recruitment gathering, a mysterious figure named Garou steps forward, claims to be a monster, and immediately launches a brutal attack on those present. Garou's assault on the Hero Association only grows worse as he overwhelms every hero he faces. It eventually comes to light that he was once the top student of the famous martial artist Silverfang, though his true intentions remain a mystery. Regardless, this powerful adversary seems impossible to defeat. Intrigued by the enigma of this new threat and motivated by a cash prize, Saitama decides to join a peculiar martial arts tournament. As the tournament unfolds and Garou's attacks persist, a massive danger arises that threatens all of humanity. Could this be the devastating catastrophe predicted by the seer Madame Shibabawa?