Saitama vs. Orochi

You... do not appear to be useless trash that can be ignored...

Saitama vs. Orochi was the battle between the B-Class hero Saitama and the leader of the Monster Association: Orochi.

Prelude
After being defeated by Tatsumaki, Psykos calls out to Orochi to save her but to no avail. She 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. 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 starts introducing himself, but Orochi attacks Saitama with one of his dragons. As he attacks, he thinks about how 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, concluding that if Saitama isn't destroyed here, he will become extremely dangerous to the Monster Association. Saitama narrowly dodges the attack. The hero angrily notes that the attack burned his cape. Overgrown Rover manages to regain his consciousness and witnesses Saitama and Orochi fighting. Orochi orders him to eliminate Saitama, but the dog immediately recognizes the hero and flees in terror. Orochi is shocked that Rover disobeyed a direct order from him. Saitama says that "Orochi is definitely a monster", and says he won't need to hold back. Orochi hears this statement and contemplates, realizing that Saitama wasn't bluffing and he did indeed go easy on Overgrown Rover. He says that the monster cell in his body has grown restless. He begins to compress his body into a more compact humanoid form more suitable for battle as he prepares to fight Saitama.

Orochi begins to monologue about how Saitama has truly piqued his interest as he's managed to reach the pinnacle strength possible for human beings and how this strength will fare against Orochi, looking forward to the duel. Orochi starts to introduce himself, but Saitama cuts him off, stating that on the contrary, he has no interest whatsoever in who Orochi is, but tells him that nevertheless, he'll fight, though 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 and Psykos, who protect themselves with psychic barriers. The energy blasts also elevate the terrain below Z-City and cause the buildings to rise, as well as destroy many other 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 some of his dragons to try and stop Saitama, but Saitama destroys all of them. Orochi and his remaining dragons 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. 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.

Aftermath
Gyoro Gyoro sends one of her eyes to look for Orochi only to find his remnants, confirming his death. When looking for the hero that killed him, she sees Saitama who mistakes her eye for a bug and crushes it by clapping his hands together. When Gyoro Gyoro notes on Saitama's bald appearance, Tatsumaki wonders if she's referring to Superalloy Darkshine, giving him the credit for Orochi's defeat.