A/N Section: By popular vote, Saitama!Deku is the winner!

Other divergences from MHA canon: From a Watsonian perspective, Izuku has his GED after he found out that UA didn't take quirkless people. From a Doylist perspective, I didn't want to write a school setting. A hero license can be awarded to anyone 15 and over, to make room for extremely impressive students, such as All Might and Genos, although he is home-schooled by Kuseno, rather than attending a high school.

Other divergences from OPM canon: Genos is 16, rather than 19 to make the age gap less weird. There will be no shipping, but I felt like making Genos his canon age would make interactions between him and Genos slightly awkward. He also has a weak fire Quirk that was enhanced by Kuseno's cyborg modification. Kuseno himself has an intelligence Quirk. Genos is also already registered as a hero, because we can't do the Exam Arc due to Izuku's quirkless status. I also didn't want to have to deal with Quirk laws surrounding Genos' fire, so I just had him be registered prior to the story.

I know I said that I would diverge from One Punch Man here, but I'm going to introduce Genos here, and have this story's equivalent of the Saitama vs Genos, then we'll get to original content. I will be skipping over MOST of the other One Punch Man arcs, but I will include one after this. I won't spoil which one, mind you.

Izuku woke up to half of his apartment building completely annihilated. A large hand swept through his room, knocking him through several buildings, before his head started to bleed from impact. A creature stood above him, a large, muscular creature with a darker complexion. He had multiple red eyes and one gigantic maw, with a circular ring of teeth.

"Just what are you?"

"What? That's rude, considering that we are the true Earthlings," the creature spoke.

"We?" Izuku replied, simultaneously excited and horrified.

"I believe that you would call us... Subterraneans," the creature, now known to Izuku as a Subterranean, said.

"We suffer from overpopulation; therefore, we must now conquer the surface. We have already killed 70% of the surface dwellers. Even the one you call All Might is dead."

"I won't... let... you... take the surface!" Izuku choked out.

"Then die."

Izuku landed a serious punch, killing the first Subterranean, but more came. He leapt between each one, annihilating all in one shot. The battle found itself at a bridge, and Izuku briefly lost his footing, providing an opportunity for a devastating shot to the solar plexus, smashing Izuku into a building. A glint in Izuku's eyes morphed into a menacing green aura, destroying the bridge and setting the surrounding area ablaze.

"This feeling..." Izuku muttered.

Before he could finish his thought, a more massive Subterranean with gigantic arms and four swords rose out of the ground. It towered over all but the tallest remaining buildings.

"I see that you have taken care of my children..." The Subterranean King remarked.

"It's the feeling... of a true fight!" Izuku leapt towards the king, getting ready to throw a punch at 100% power. Right before their fists were to collide, Izuku heard a peculiar sound...

RRRIIINNGGG! Izuku punched his alarm clock through the floor with a disappointed expression on his face.

Izuku then hesitated before leaving his bed.

"What's that sound?"

He opened his window and saw a group of villains with shovels calling themselves "Subterraneans". By the looks of it, they had been out there all night, which likely inspired the content of his dream.

Excitedly, Izuku jumped out and landed a normal punch, KOing one of them. To his surprise, the others left a white flag with the word "Sorry!" written on it and ran away.

Genos noticed some cows, dying in a field. He examined the corpses, and found many puncture wounds riddling them, coupled with extreme blood loss.

"Mosquitoes."

Izuku was at his house, watering his flowers, when a villain attack alert sounded on the television. Apparently, a giant swarm of mosquitoes had been flying around the city, and the coordinated nature of the swarm suggested an Insect Control Quirk.

"Eh, sounds like a nice matchup for Endeavor," he remarked.

Izuku started monologuing about his situation to himself.

"I... have become too strong. There is not even a sign of this world's evil dying out at all, meaning that my actions as a hero... haven't even made a difference. If anything, villains have become even more common. That doesn't matter to me, though. I started as a hero so that I could save people, but I quickly learned that it's impossible to save everyone, no matter how powerful you are. So, I turned to obsessively fighting villains as an alternative. Nowadays, I admit that I am mostly acting as a hero for excitement. It's what had saved me when I lost the will to live... After I was rejected from UA due to being Quirkless. I am facing a huge problem, though. My emotions are weakening day by day. I don't feel excitement, or joy, or even anger, either. Could it be... that I have lost something essential as a human in my quest for infinite power? Every fight now ends in one punch. No matter who I come up against... it's as easy as swatting insects. My weaker self desired power, but now I desire nothing."

A mosquito flew through the window.

"Yeah, as easy as swatting a fly. I feel nothing when I succeed"

Izuku used a Serious Clap, thinking that he killed it, yet the air pressure from the clap knocked the mosquito out from between his hands.

"Damn... mosquitoes!" Izuku gritted his teeth.

CLAP

Another clap missed the mosquito. Izuku repeatedly clapped, missing over and over again. He glared at the mosquito with a dark look in his eyes and readied even more slaps to the annoying insect.

Both Endeavor and Genos made their way to the epicenter of the swarm, as the mosquitoes attempted to drain more and more creatures. When they made it, they noticed that there was, in fact, a human at the center.

Mosquito Girl swayed her body, gesturing for the mosquitoes to come closer, her groaning in quite a suspicious way each time she gained more power.

"I see... You drain the blood of innocents, then use your Quirk to take it all for yourself."

"Hmm...? I guess we have our next meal. The last one wasn't nearly enough to satiate me, go drain that boy."

A swarm of mosquitoes formed the shape of a spike, driving themselves towards Genos at blinding speeds.

"Incinerate."

The mosquitoes were wiped out almost instantly, but more came from surrounding trees, replenishing the swarm.

"So you're a robot? No matter, Endeavor probably has some juicy blood for me to drain." Mosquito Girl smirked and launched her swarm at Endeavor."

"Filthy villain scum. PROMINENCE BURN!" Endeavor let out a massive amount of fire, scorching swathes of mosquitoes.

"What are you doing here, civilian? You know that you have to register yourself as a hero to use your Quirk," Endeavor stated.

"I am recently registered as the number 11 hero, Demon Cyborg," Genos replied.

"Number 11 already? You must have an impressive Quirk."

While the two heroes were distracted, Mosquito Girl ripped off Genos' arm, but she also had her legs sliced off by a Flashfire attack from Endeavor.

"The townspeople may be hiding, but there are many animals around here than can fuel me."

"Come, my children, and feed me that delicious red nectar!"

Mosquito Girl powered up into her monster form and quickly overwhelmed the two heroes with a flurry of attacks.

Izuku followed the mosquito into the street, holding bug spray and attempting to kill the mosquito with it. The mosquito led Izuku to the swarm of its brethren, them forming a gigantic orb. Izuku then opened his mouth, gawking at the sphere, and as a consequence, the mosquito flew down his throat, leading to Izuku coughing madly. He then spotted Endeavor clearing out the swarm of mosquitoes, while Genos went toe to toe with Mosquito Girl. She eventually overwhelmed Genos, though.

"...Damn it. All of that, just to be defeated before I could avenge my village. The only thing I can do now is... self destruct." Genos' core glowed a brilliant shade of blue and started expanding. Before his core could explode, Izuku smacked Mosquito girl lightly, all of the blood absorbed being vomited up, letting Endeavor apprehend her.

"I hate mosquitoes. They... suck!" Izuku said, chuckling at his own terrible pun.

"Now, I know YOU aren't registered," Endeavor grumbled, his Quirk flaring.

"Oh, I don't have a Quirk," Izuku casually said, leaving Endeavor too dumbfounded to even speak.

Izuku walked away, but Genos started mumbling to himself.

"Who is this naked boy? And why is he so powerful? What is the secret to such... Limitless strength!?"

"Wait, what do you mean, naked? AAAAAAAHH!" Izuku noticed that the swarm had shredded his clothes.

"I'd better get home! Damn, I wish I had brought my hero outfit!"

"Wait! What's your name?" Genos exclaimed.

"It's Izuku, what's yours?" Izuku replied, attempting to act cordial.

"I am a cyborg fighting for justice, too! My name is Genos, but you may know me as my hero name, Demon Cyborg!"

"Oh, you're Demon Cyborg?" Izuku questioned.

"Yes, now will you take me as your disciple?"

"Sure," Izuku said, hoping to get this annoying cyborg off of his back, "Be at my house at exactly 3:35 PM tomorrow."

"No way that this guy actually shows up," Izuku chuckled to himself.

"You really think this Izuku kid is that strong?" Doctor Kuseno asked.

"Yes, he saved my life, after felling Mosquito Girl with a single punch."

"I do have some upgrades for you, which may help you prove a match for this Izuku. I am skeptical, but I trust your judgement, Genos."

~~ 3:35 PM, the next day ~~

Izuku returned from his daily shopping trip to see Inko looking terrified in the corner of the room, while Genos stood in the center.

"Oh. You actually showed up."

"IZUKU! Who is this strange man in the house?"

"Um, he's a hero."

"Wait, you're that new guy, aren't you?" Inko said.

"Affirmative," Genos replied.

"Genos, we can talk upstairs. Let's go," Izuku said, practically dragging Genos up the steps. When they made it to his room, which had a distinct lack of All Might merchandise, Genos spoke.

"Ah, teacher Izuku! What is my first lesson as your disciple?"

"Could you quit calling me teacher? It makes me feel weird," Izuku stated.

"Master!"

"Don't call me 'master' either."

Izuku slid some tea over to Genos.

"Go home when you're finished drinking. I'm not looking for any disciples right now."

Izuku then noticed something... off about Genos.

"Wait, how are you in one piece again?" Izuku asked.

"Since my body is artificial, it is easy to replace my parts. That reminds me, teacher, what artificial parts do you use?"

"I don't use any."

"Then what's that skin-colored armor coating your body? I heard that you told Endeavor that you're quirkless, but you seem to have a strength quirk augmented by artificial parts."

"It's called skin."

"Then... That would mean... You're quirkless, despite being so young."

"What's wrong with that? What the hell is your problem anyway!?" Izuku's temper flared after being insulted for his Quirk status. Genos looked like he had been waiting for him to ask that question.

"My problem? Do you wish to hear my story, master?"

"Uh, no thanks."

"A long time ago, four years, exactly, I was twelve years old and still a normal human being with a weak fire quirk. Even in this harsh world, I had a pretty happy and peaceful life with my family. But one day, a mad cyborg attacked our town suddenly. He had lost his mind, likely due to a faulty brain transplant into his cyborg body. After destroying my entire town, killing everyone in it, despite some moderately powerful Quirks, he mysteriously disappeared. Only I was spared, but as I was a meek twelve-year-old boy back then, I would not have survived the wilderness if the super-intelligent Doctor Kuseno hadn't saved my life. It turned out that he, too, was pursuing this mad cyborg. I begged him to transplant my brain and Quirk factor into a cyborg body. I made a promise to Doctor Kuseno to find that cyborg and one day stop him. That's where you came in. The life that was saved that day by Dr. Kuseno was once again saved by you. Th-"

"ENOUGH ALREADY! KEEP IT TO TWENTY WORDS, OR LESS!" Izuku practically screamed, sick of Genos' story.

"Yes, master!"

The UA entrance exams played out as normal, sans Izuku's involvement. Bakugo ended up winning; however, the teachers weren't impressed with anybody below 19th place in the exams.

"None of these seemed like UA material from what we saw," All Might said, frustratedly.

"I do have a recommendation, then," Eraserhead replied, "Shinso Hitoshi, from the General Education course would be a good applicant."

"From Gen-Ed, really?" Cementoss questioned.

"He has a mind-control Quirk, ineffective against robots. He would be a valuable asset to any UA class," Aizawa got really close to All Might's ear, "And would probably do better against All For One than you did," eliciting a gulp from Toshinori.

~~END~~