Earth is saved by heroes for the time being, yet the large-scale conflict between the Hero Association and the Monster Association is far from concluded. The perilous hero hunter Garou remains at large despite capture attempts, and the Monster Association has kidnapped a prominent figure, plunging the Hero Association into chaos. Facing a strict deadline for the rescue, the heroes depart to locate the monsters' hideout. Despite being severely injured, Garou is recruited by the Monster Association with the aim of integrating him into their leadership. To climb the ranks, the hero hunter must first demonstrate his willingness to abandon his humanity by killing a hero. Garou quickly finds a target, but that individual happens to be the unaware Saitama, who effortlessly knocks him unconscious. This humiliating loss leads to Garou being labeled a traitor by the monsters. Furthermore, the next confrontation between the two associations draws near rapidly. As both sides prepare to employ any tactics and utilize any pawns available to them, the world's safety rests in their hands.