( Before starting I know shit next to nothing about pain tolerance, either way I major in bullshitting not science )
The experimenting started when Izuku got his quirk, super healing
He can heal himself and also the others so it was pretty nice except it all wasn't all fun sunshine and rainbows, whenever Izuku scrapes his skin, or gets a paper cut, or gets hurt his healing comes up as if the spot that was hurt was being burnt close while he's awake with nothing to ease the pain with, his doctor said that his quirk works like a doctor, if a doctor heals someone they usually numb the patient first so that they won't feel pain but in Izuku's case he's both the doctor and the patient, and would doctors make themselves fall asleep in a middle of surgery?
Izuku learned that no, don't do that, it didn't help at all that Izuku didn't really have a lot of balance in his 4 year old self, so instead of acting more careful, Izuku decided to take it upon himself to make himself tolerant to the pain
When Inko wasn't home Izuku would roll down the stairs, bang his head on counters, hit himself with pans, and trip as much as he can, his pain tolerance is getting a bit higher but after sometime he wasn't able get it higher than that because he keeps on feeling the same thing over and over again, and it stopped growing after that, it still hurt, Izuku's plan was to be 100% tolerant
So he went up to his childhood friend and with the most sincere voice and face in the world, he said
"Please punch me as hard as you can Kacchan!"
Katsuki stared blankly at him weirdly for a few minutes, weird because Izuku always runs or scoots away when Katsuki got too close, but eh, extra practice, Katsuki smirked before punching Izuku as hard as he could, the other lackey's of Bakugou laughed as Izuku felt a new level of pain and while it hurt a lot he still managed to look starstruck towards Katsuki because wow, who knew that all he needed was to be a punching bag for his friend?!
Katsuki stared at him weirdly as Izuku who he just punched yesterday, came up to him with amazement in his eyes
"Punch me again Kacchan!"
This went on again and again and again and again
"Kacchan please punc-
"Stupid Deku its been months! Aren't you getting tired? I mean sure your quirk heals it up but why the heck are you even doing this?!"
"It hurts alot when I heal so I thought it'll be good to get used to it while I'm still young! So I can become a hero like Kacchan!"
This time Kacchan punched him with his explosion quirk
Izuku got a scar from that but when he got home the skin over it seems to be forcibly removing the scar by repeatedly peeling over and over again
The next day the scar was barely even there, Izuku with starts in his eyes said again
"Punch me again Kacchan!"
"No!"
Katsuki pushed Izuku as far as he can and ran, Izuku regained balance after awhile and started running and chasing around Kacchan with stamina he sure wasn't there before, Katsuki face looked blank, it was fun at first having a punching bag but now Katsuki feels guilty about punching the fuzz of green chasing him around because the punch made a scar and sure while it was slowly being removed, heroes don't just hurt people should've thought of that moths ago Katsuki, he thought to himself
Izuku stopped asking Katsuki to punch him after that but week after, Katsuki's jaw dropped
There was a pencil imbedded at Izuku's arm
"Deku why do you have a flipping pencil in your arm?!"
"Wha... what are you talking about Kaccha- Ah! Kacchan help!"
"Stay still stupid Deku! This is what you get when you up your pain tolerance too much you can't feel anything anymore!"
"Wahh! Kacchan it feels weird just pull it out!"
"Its already out you dummy!" Katsuki took notice that one of his lackey's was whistling innocently and shifted unto what he was holding, it was a case full of pencil, well almost full there was one missing
The next day, Katsuki spots Izuku with a shit ton of things sticking out of him, fingernails, nails, arrows, needles, icicles and a poison needle, and Izuku didn't even seem to know why the heck was Kacchan looking at him so weirdly
Katsuki got close just to remove all of them from Izuku's body, Izuku is just happy to have his friend so close to him even if all Kacchan was doing was removing the things that are sticking out of him
Since that day, Deku got himself a new nickname
'Dummy Deku'
But Izuku was smart, his scores are always just a point lower than Kacchan's so he was confused
"Its because you make a good punching bag, dummy"
"Oh.. OH I get it Kacchan! Haha! How did you know that?"
"Of course, I'm the best!" Katsuki started boasting about himself while Izuku looked at him with eyes that can only be seen when he's watching All Might videos
Inko's reaction was rather different
Inko didn't know what happened, all she knew was that Izuku was just eating dinner happily until he hear some noise from the back and turned to look, Inko's stomach did a flip after seeing a pocket knife clearly attached to Izuku's back except instead of it hanging there it was inside Izuku's back, the pocket knife might be small but it looked big on Izuku's little body
Inko panicked and was about to call the hospital until Izuku grabbed the phone from her hands and casually removed the knife as if its just something that happened often and he grew used to it, and then continued eating dinner
"Izuku?"
"Yes mom?"
"Uh.. aren't.. when did you have that?"
"Oh I'm not sure! But free knives mom! How do you think the random knives get there?"
Inko paled
Katsuki didn't know why but suddenly his old hag of a mother, after receiving a phone call, stated that Katsuki will be Izuku's bodyguard, at first Katsuki was understandably angry and annoyed but then realized just how fun it is because random delinquents had a habit of sticking their knives in tiny animals or anything that resembles it
On the news the day after that is that a bunch of delinquents got blown up, not sure if its just a mistake or a villain just yet, it definitely wasn't a villain, Katsuki thought
"Hey Deku?"
"Yes Kacchan?"
"Let me punch you" Without waiting for an answer Katsuki blasted Izuku with his quirk the best he can
Izuku stood there not knowing what happened or why his shirt wasn't on anymore
.
At the age of 10 Bakugou got into an accident
At the same day of the accident he recovered
"Isn't this cool Kacchan? The doctor said it might take months but I made it go away quickly!"
"Y-Yea.. whatever" Katsuki was kinda amazed "Glad to know you're less useless than I thought" Izuku grinned
"Thanks Kacchan!" Izuku kinda sagged, he felt a bit sleepy from that
"That wasn't a compliment you fucking nerd"
And now its become of a tradition that Izuku will always be the one to heal Katsuki's wounds, big or small he'll go to Izuku to have them healed, his excuse
"It'll heal faster this way and I can kick more ass!"
Izuku didn't mind, he's happy that his quirk is growing and so is Katsuki's, but he always felt sleepy after using his healing on others, he yawned and fell but Katsuki caught him and plopped him on the sofa, Inko chuckled, how sweet
.
At the age of 15 they were asked what they wanted to be in class, just discuss it infront, you know the usual, most of them said heroes of course, by most I mean everyone, atleast until Izuku came up front
"When I grow up I want to be a lawyer!"
Everyone stared at him for a few minutes, blinking until Katsuki broke the silence
"Izuku what the fuck"
"Wha.."
"Shut up shitnerd you're going to the hero course!"
"But but, Kacchan haven't you seen what the lawyers do-
"Atleast be a doctor or something you shitty fucking nerd!"
.
It was no surprise when Katsuki managed to get into UA easily
"Kacchan I wanna be the boy with spikey hair here!"
"Are you basing off your ambitions off a game?! What about All Might?!"
"I'm gonna defend All Might from the Law and give him justice!"
"He is justice, you piece of shit!"
Izuku didn't know what happened but he was dragged by Kacchan into UA when he didn't even the sign the papers, Izuku then realized that in these exams alot of students can actually get hurt, he was sure he already healed atleast 30 of them and to be honest he's getting kinda sleepy and dizzy, it didn't help that Katsuki was dragging him around to kill robots
Izuku then just realized he went in at the wrong time at the end of the exam
"Kacchan! I was supposed to get in the General Education department!"
"Who cares?! You topped, look" Katsuki pointed at the rescue points that Izuku got, atleast 120 points for him while Katsuki still topped because oh boy he killed lots and lots of robots
"But Kacchan I want to be sidekick! Not a hero!"
"Why the fuck would you want to be a sidekick?!"
"So I can always work with Kacchan when he becomes a hero! Kacchan will choose me as his sidekick right?!"
"S-SHUT UP YOU SHITNERD! JUST BE HAPPY THAT YOU TOPPED!"
Izuku tried to stay to clear his name from there and get into the actual course he was going to take, he actually managed to say so, to President Mic, Mic just looked at him weirdly as Katsuki dragged him off
He took a test for the General Education course and there was no way he didn't pass it
"Yo! President Mic here yo! You're the weird student that tried to get himself removed from the heroics department yeah?! WELL LUCKY YOU, YOU'RE STAYING!"
Izuku slammed his head on the desk, damnit
Izuku didn't want to go, but Katsuki has just to be a good friend woke him up early, even washed him and got him in his uniform
Great first day
"Hey you're that boy that healed everyone! Aren't you supposed to be in the support course?"
"I know"
