Episode 24

"The Wiping of the Disciple's Butt" is the twenty-fourth episode of the One-Punch Man anime series and twelfth and final episode of season two.

Plot
Bang hits Garou with Water Stream Rock Smashing Fist and Garou counters with the same attack. Standing aside, Genos notes that Bang's mastery of the style is far superior to his disciple's, saying how the battle has already been decided. Bang gives his all, kneeing Garou in the face and slamming Garou into the forest floor. Leaping into the air, he furiously assaults his former student, punching his chest into the ground, Garou himself pondering that Bang has never fought this aggressively before and worries his death may be imminent. With the moves taken from Watchdog Man's fighting style, Garou escape the onslaught of fists and leaps around the trees, to Bang's confusion. He attempts to use Death Gatling's body as a shield, only to be kicked away by Bomb, having taken care of the monsters assisting Garou. Phoenix Man surveys the battle from above, noticing how Genos, Bang, and Bomb have defeated the monsters he sent. Knowing the consequences of disobeying Orochi, he realizes that in order to return to Orochi with Garou, Garou has to survive his battle against the heroes. Garou curses the fact that his former master is using the advantage that he is already beaten and his brother Bomb, master of Whirlwind Iron Cutting Fist, is with him to stop him. He then realizes that Genos is also there to stop him and Garou decides to kill all three in order to escape his situation.

Garou, nearing death, sees his life flash before him and reminisces on a particular memory of playing in the playground with the other kids. One of them, Tatsu, kicks another child to replicate Justice Man. When Garou notes of the potential danger of replicating the show, Tatsu orders the other children to surround Garou and insist Garou be the monster himself. At school, Garou starts a fight, tired of Tatsu's treatment of him, only for the principal to condescendingly insist Garou is the one at fault. This is the fuel that drives Garou forward and he continues to attack the heroes, splitting the ground and knocking Bang and Bomb back. As Garou prepares to attack again, Phoenix Man appears above him and blows away the heroes with gusts of wind from his wings. He grabs the Hero Hunter by the shoulders and flies away. Bang, Bomb and Genos land unharmed and see a monster helping Garou. Genos attempts to shoot the two down, ignoring Bang's pleas. Phoenix Man suddenly yells that he is taking Garou and is "leaving the rest to you". Shouting his name, Phoenix Man summons Elder Centipede, the Dragon-level monster erupting out of the ground and stopping Genos' beam from hitting Garou and Phoenix Man. With the ground splitting from the creature's enormous size, the defeated heroes nearly fall into the chasm before being saved by the three. Garou becomes angered at the monster's intervention of his fight, only for Phoenix Man to respond by telling him to be quiet and let Elder Centipede finish the battle. Phoenix Man notes that according to Gyoro Gyoro, only 4 S-Class heroes stand a chance of beating the centipede; Tatsumaki, Metal Knight, King and the very hero that nearly kill him, Blast. Garou orders him to release him only to be told to calm down and let Elder Centipede kill the heroes. Phoenix Man states that while the three are obviously very powerful, Bang and Bomb's martial arts would be useless and Genos lacks the firepower to kill something of Elder Centipede's size.

The monster charges forward and Genos retaliates by firing his incineration cannons into his face and eyes. He steps back and lets the two brothers attack. Together, they combine their techniques to create Whirlwind Water Stream Roaring Aura Sky Ripping Fist and the attack hits Elder Centipede directly, knocking the immense creature back. The duo don't let up and continue to attack but Elder Centipede hits back, knocking Bang and Bomb away and only saved when Genos stops them from flying back any further. The monster's exoskeleton cracks and falls away, only to regrow in mere seconds and a new face grows back, signaling the creature has only gained more power, despite the brother's efforts. Realizing they have no chance and the monster entering the city means civilian casualties, Genos steps up to try and stop Elder Centipede. The elder heroes try to stop him, saying how he is still young and has his life ahead of him. Genos himself remembers Dr. Kuseno's works to not push himself too far. Genos decides to fight anyway, flying to the monster and firing his cannons at its face. Genos, knowing Gouketsu, Elder Centipede and Garou are part of the Monster Association and realizes a battle like this was inevitable. The Demon Cyborg flies to the centipede's face and slashes wildly at its eyes with his arm blades. Elder Centipede reels in pain but catches Genos' leg in his mouth and bites down, then grinds his face against his body to crush Genos. Genos breaks free but is caught by an antenna and is helpless as Elder Centipede's pincers slice his body in half. However, the halves of his body soon rejoin and the cyborg flies into its mouth, breaking one of its teeth. Inside, acidic fluids nearly kill Genos but he retains enough strength to activate Ultra Spiral Incineration Cannon, burning the monster from the inside. Elder Centipede wretches and spits out Genos, landing hard in the dirt away.

Despite the hero's efforts, the exoskeleton fuses again, dissipating the heat and rendering Genos's attack useless. Elder Centipede tries to crush the fallen Genos, only for him to be saved by Bang. Garou, still in Phoenix Man's grasp, ponders the battle doesn't end right, that they are his prey and defeating them would make the Hero Hunter the greatest object of fear. Phoenix Man laughs at this, stating that Garou doesn't have what it takes to defeat Elder Centipede, let alone the upper echelon of the Monster Association. As Bang and Bomb run away from Elder Centipede, Genos thinks what he is missing that can beat the monsters like him and he cannot simply watch a battle. When Bomb notes that they are luring the creature to the city, Bang drops the wounded Genos next to a tree and takes off his shirt, deciding to fight Elder Centipede even at the cost of his life. As Bang takes a stance and prepares to make a last stand, King appears in the forest. With a megaphone in hand, he calls out to Elder Centipede and states that he has brought Blast with him. Knowing his grudge against Blast, King insults and goads Elder Centipede into attacking. King remembers a plan to bring the creature to his location to prevent more city casualties. Elder Centipede charges forward, ready to kill King. King calls out to Saitama to save him and he arrives in the nick of time. Preparing a Serious Punch, Saitama hits Elder Centipede square in the face, killing him and causing his body to disintegrate.

As Saitama and King collect themselves, they see Bang, Bomb and a heavily injured Genos. When King notices how Saitama seems refreshed, he responds by saying that throwing the punch help relieved his anger from his consecutive losses to him. Genos appears his master and asks for what he is lacking. When Saitama suggest he is lacking power, Genos furiously thanks him for his advice, causing King to worriedly tell him not to use Saitama as an example. Genos tells himself how his battles have shown him the way and what true strength is. Saitama humbly suggests going home.