"-well if you weren't such a stubborn ass-"
"-explode your fucking face, maniac-
"AHEM." Aizawa loudly cleared his throat, drawing the attention of the entire class including Midoriya and Bakugou.
"Ah shit," Bakugou cursed.
"Now-" Aizawa started before being cut off by a squeal from Midoriya who had just seen the teacher.
"HOLY HECK IT'S ERASERHEAD!"
Aizawa wasn't expecting to be recognized, typically his status as an underground hero kept him out of the public eye which was exactly how he liked it. Still, he refused to show any surprise and instead simply nodded. "Eraserhead is my-"
"You know this hobo?!" Bakugou asked Midoriya, interrupting Aizawa once again.
Aizawa glared at the boy and activated his quirk, his red eyes glowing threateningly. It wasn't necessary. Midoriya had already shushed him loudly and Bakugou recoiled before rolling his eyes.
"Geez. Sorry."
The way he said it implied that Bakugou was actually not sorry, not even a little bit, but Aizawa decided to let it slide. "As I was saying, I am Aizawa Shouta, your homeroom teacher," He turned to stare at Midoriya, "Also known as pro hero Eraserhead."
There was quite a bit of whispering following that declaration, the loudest was of course Bakugou announcing his disbelief that "a washed-up stiff like that could possibly be a hero" followed by Midoriya's rambling mutters that were only comprehensible to himself. Even Bakugou, having known the boy for his entire life, was only able to catch about one in seven words. This was not very useful as it's very difficult to understand a one-sided conversation when six-sevenths of the sentence are unintelligible.
Aizawa sighed. Twelve seconds into knowing these two and he was already mentally weighing the pros and cons of retirement.
"Quiet, please." The class compiled. "Your gym uniforms are in that box right there." He gestured to the front of the room. "You have 10 minutes to get changed and meet me at the testing grounds. Do not be late."
And with that Aizawa did a 180 and walked out of the classroom as the children scrambled madly to find their outfits in his peripheral vision.
He wondered if it was too late to beg Nedzu for a raise.
Aizawa found his will to live shrinking exponentially throughout the testing.
There were many reasons for this. Partially it was because Bakugou was constantly declaring his superiority and how he was going to beat Midoriya with a confidence that was, if I am to be honest, downright terrifying.
Mineta going around harassing all the girls was also not helpful. Aizawa vowed that if the pervert got last he would make good on his promise to expel him.
There was also the slight issue of Midoriya.
That's a lie, Midoriya was the main issue, nothing slight about it (Aizawa suspected that would be the case in most situations). The boy seemed to sacrifice his limbs the same way one might throw out old leftovers; without concern and with only minimal deliberation.
"If I use my left leg for the long jump then it will be harder to run the 50- wait I could just use my right and jump the whole thing- but then my sideways jump score will be trash- I can dislocate my back for the toe touch to make up for it though- and then my left hand for the grip strength and my right for the softball throw- yeah that should work…" Aizawa struggled to hear Midoriya's mutters and even after getting closer he doubted he had heard correctly, until he watched with his own two eyes as Midoriya passed each test with both flying colors and broken bones.
It still took several minutes for Aizawa's brain to catch up to his eyes. Halfway through the testing, Midoriya was already limping with two broken legs and what appeared to be a completely shattered left hand. And the kid just- was fine? Literally no sign of pain and even Bakugou acted like it was totally normal that his friend was completely broken, only stopping to tell him how he was definitely going to beat him.
The rest of the class seemed quite baffled upon watching Midoriya as well. However, they considered the fact that one of their classmates had both a bird head and a sentient shadow while another was quite literally invisible and decided that a boy who broke all his bones in a burst of super strength wasn't that weird.
This reasoning did not help Aizawa from feeling that the entire situation was extremely confusing. He later internally blamed this confusion for causing him to have an idea which in hindsight was perhaps not entirely smart.
In his defense, he was only aware that Midoriya had a strength quirk as his file did not list any specifics such as his inability to feel pain or the healing aspect of his quirk. This meant that Aizawa was privy to only the knowledge that his student was knowingly breaking his own body in order to pass what should have been a very simple placement test.
Still, using his quirk on the boy was perhaps one of the worst things he could have done.
But let me reiterate that Aizawa should not be blamed for what followed, in his mind he was simply doing what was the sanest option in an insane situation; stopping his student from shattering his one remaining arm during the ball throw.
Now the simple fact was that Midoriya was now in possession of two separate quirks, Adrenaline Rush and One For All. While technically speaking the two had merged to become Hysterical Strength, Midoriya still thought of them as separate. Perhaps that is why Aizawa was only able to erase one of them as he activated his quirk.
Midoriya threw the ball with literal superhuman strength as he activated One For All. Unfortunately, he did so only a fraction of a second after Aizawa activated his quirk in an attempt to stop Midoriya from hurting himself more. This had the opposite effect of suddenly erasing the effectiveness of Adrenaline Rush and leaving Midoriya with four broken limbs and the feeling of excruciating pain for the first time in a decade.
This, as you can imagine, was not entirely pleasant and Midoriya reacted in the typical manner for those in immense agony.
He screamed.
The scream was loud and long and continued even as Midoriya collapsed to the ground like a rag doll. It suddenly dissolved into a long string of garbled half profanities. "FrigingHECKdagnabit-"
Realizing that something was very wrong Aizawa immediately blinked, stopping his quirk. This was actually mostly an instinctual action as inwardly he was freaking out as he realized he had just killed a kid.
He hadn't. And even if he had it wouldn't really be that big of a deal, after all, Midoriya is immortal. Although on that note, it remains to be seen if he would actually come back to life if he was to die while Aizawa had his quirk active. Forgive me for not wanting to test that.
As soon as his quirk cut off the screaming did too. "So THAT'S pain! Wow! What a rush!" Midoriya jumped to his feet, seemingly back to normal. His smile faltered a bit. "I don't think I actually liked that."
"The hell happened?!" Bakugou yelled at him. He sounded quite angry but in actuality, he was simply concerned. It is very easy to mix up these emotions with Bakugou as to an outsider there is no discernible difference.
Aizawa was still rather shocked at the unexpected situation, a common symptom of Midoriya's trademarked teacher trauma, and made no move to explain. Luckily Midoriya jumped in right away to answer.
"That's Eraserhead's quirk! Isn't it cool? It was even able to override my quirk's pain suppressors." The last end of his sentence was directed at Aizawa. The teacher realized that Midoriya was trying to help him by offering an explanation for his reaction. It made sense, a pain suppressant aspect of his quirk explained why he hadn't seemed to mind getting injured.
Still- "Your approach to this testing is illogical. Do you intend to become incapacitated and have someone save you?"
"Mr. Aizawa, sir, I'm simply trying to show you what I can do. Also, as a part of my quirk, I can heal myself when I need to."
"...That wasn't on your file." And it really should have been. Aizawa thought. He was going to have a talk with whoever decided that it would be a good idea to ignore that crucial information and nearly cause him to have a heart attack.
Midoriya shrugged. "Well, I can. I don't really need to worry too much about being safe or taking it easy because thanks to my quirk there's not much of a downside to going full on plus ultra all the time."
Aizawa did not have a proper rebuttal to this and still being a little rattled as it was he simply sighed and put a hand to his temple. "Fair enough."