Saitama vs. Orochi

Saitama vs. Orochi is the battle between the B-class hero, Saitama, and the leader of the Monster Association, Orochi.

Prologue
After Psykos is defeated by Tatsumaki, Psykos calls out to Orochi to save her. Tatsumaki remembers that name mentioned before, and Psykos asserts that while she's the military advisor, Orochi is the boss of the Monster Association, and that even as his creator, she cannot accurately gauge his power. Psykos wonders why Orochi is not coming to assist her, for she managed to obtain absolute control over him from years of brainwashing during his transformation as a monster. Unbeknownst to her, Orochi took notice of Saitama being able to defeat Overgrown Rover. Using his dragons, he lifts himself up several floors of the Monster Association Headquarters and spews cascades of fire that cover his entire chest, while several dragons slither out of his body as well. Saitama goes over all of the odd things he's seen so far: a pair of streakers, a dog, a cat, and now, this monstrosity, and wonders how something like this could live underneath his house. Orochi says he doesn't know how Saitama managed to get in, but he can tell that Saitama is not useless trash that can be ignored.

Saitama tells Orochi that he's someone who lives above, and all the noise has been bothering him. Orochi then attacks Saitama with one of his dragons. As he attacks him, he notes to himself that he came because he sensed the abnormal impact from Saitama, and realizes that although he wasn't registered as a threat by the Monster Association, he is a major, unexpected existence. He also concludes if Saitama isn't destroyed here, he will become extremely dangerous to the Monster Association. Saitama overhears this and asks Orochi if there is indeed a whole group of monsters living below. Orochi attacks Saitama again with a blast of energy. Saitama narrowly dodges the attack. The hero angrily notes that the attack burned his cape. While the battle is taking place, Overgrown Rover manages to regain his consciousness and witnesses Saitama and Orochi fighting. Orochi notices the canine's presence and orders him to eliminate Saitama. But upon seeing who Orochi was referring to, he immediately recognizes Saitama and flees in terror. Orochi is shocked that Overgrown Rover disobeyed a direct order from him and asks Saitama what he did to him. Saitama simply replies that he beat him up, and changes the subject to how Orochi burned his cape. Saitama also states that Orochi is definitely a monster, and that he won't go easy on him this time. He then tells Orochi to get prepared for a normal beating. Orochi hears this statement and realizes that Saitama wasn't bluffing and he did indeed go easy on Overgrown Rover. He also says the monster cell in his body has grown restless, and deduces that this is also the man who was behind the deaths of Gouketsu, Elder Centipede, as well as being the culprit behind the rumored monster in City Z. However, instead of being frightened or intimidated, he is actually excited, not having been this excited in a long time. He begins to compress his body into a more compact humanoid form as he prepares to fight Saitama.

Orochi begins to monologue about how Saitama has truly piqued his interest as a human who's managed to reach the pinnacle strength of living organisms. He also wonders how this strength will fare against Orochi, looking forward to the duel. With this battle, he wonders if it will awaken the faint emotions and sense of self that is slipping away. Orochi continues by declaring himself as the greatest natural enemy mankind has ever faced, but before he can finish, Saitama puts a hand up and interrupts him, stating that on the contrary, he has no interest in Orochi whatsoever. The bald hero says he's tired of hearing these self-introductions, reminiscing of his several previous foes, and tells Orochi he's fought several monsters like him, and that he is no different, assuring Orochi he'll still be defeated in one punch. Orochi gives no response, and Saitama tells him that nevertheless, they'll fight, but he's not expecting anything.

Battle
Orochi and his dragons on his left hand strike with the newly-learned Water Stream Rock Smashing Fist. However, Saitama manages to kill all of the dragons with his punches. Orochi's dragons on his right hand fire several beams of energy. The force of the dragons combining their energy beams creates a huge blast, as well as creating several lightning bolts. Throughout the Monster Association headquarters, these bolts of lightning strike several heroes, such as Atomic Samurai, who blocks the bolts with his sword, Bang and Bomb, who redirect or destroy the bolts with their respective martial arts, and Tatsumaki, who protects herself and Psykos with psychic barriers. The energy blasts also elevates the terrain below City Z and causes the buildings to rise, as well as destroy many buildings in the process. While this is happening, a train on the metro system feels the shockwaves of the attack. The conductor of the train puts the brakes on the train and notices the huge circular path in front of them that destroyed the train track. They also notice a figure blur past them, and that figure is Saitama, who is running towards Orochi. The hero then jumps up and prepares to strike Orochi's head with a single punch. The Monster King uses his dragons to try and stop Saitama, but Saitama destroys all of the dragons. Orochi and his remaining dragons all prepare to finish Saitama with a combined attack, and release a combined energy blast that goes downward. Unfortunately for Orochi, Saitama manages to power through the energy blast and punches Orochi, destroying the monster's body.

Aftermath
As Orochi's head and his broken body are floating in the air, Orochi asks Saitama what he just used. Saitama replies that it was simply a normal punch. As Orochi's head and the rest of his body fall down the pit, the monster realizes that at that moment, he is feeling terror. Saitama watches from a ledge as Orochi falls down to his defeat, making the bald hero the victor once again. Orochi's fate remains unclear.