One Punch Man Season 2 shifts focus from Saitama's mundane life to the rise of the Monster Association and the emergence of the "Hero Hunter" Garou, a former hero obsessed with becoming the ultimate monster, leading to chaotic battles where Garou fights heroes and monsters alike, while the Hero Association struggles with increased threats, culminating in the major fight against the monstrous Elder Centipedo, which Saitama ends with one punch, and Garou's transformation into a true monster under the guidance of the mysterious Orochi and Phoenix Man, setting up future conflicts.