HEY GUYS, WHAT IF ALL MIGHT GAVE HIS HAIR TO EVERYONE HE WANTS TO ADOPT!!!!
And before you tell me "That's a powerful quirk and he knows how serious it is and Blah Blah Blah," LISTEN!!!!
It started with Izuku and Mirio. He basically adopted Izuku, but then was like "let's try and meet with Nighteye after all" and meets Mirio, and He Loves Both of Them, he dads out like "WELL IF I CAN HAVE ONE MENTEE, I CAN HAVE TWO!!!" And gives Mirio his hair then and then gives Izuku his hair later.
When Izuku gains the power of ofa, it's still the exact same amount of power, because Science Shit and DNA inheritance stuff, like with normal sons and daughters.
Thing is, Nighteye finds out via Nezu, so one day All Might gets called to the principal's office and Nighteye's like "WHAT IS YOUR EXCUSE!" and All Might, without missing a beat, goes "MIDORIYA-SHOUNEN IS MY SON! HE MAINLY TAKES AFTER HIS MOTHER!"
Then he thinks "oh shoot I'm really pulling this, huh?"
But of course, both Nezu and Nighteye have lived with Yagi for long enough to know his tells. Nighteye's like "truth plz" and All Might breaks down going "he's so Smoll and precious I wanted to let him be happy he's so cute omg".
Like he doesn't notice the feral energy that's Izuku punching through walls.
Nighteye's like a scandalised housewife and goes "WHAT ABOUT MIRIO?!" and All Might exclaims "HE'S ALSO REALLY AWESOME AND WHOLESOME HOW COULD I NOT ALSO HAND HIM MY QUIRK?!"
But then All Might starts teaching.
"Iida-shounen could get hurt if he isn't powerful enough!" All Might reasons, using his superspeed to slip the end of his hair into Iida's lunch, "Ashido-shoujo's Acid would work really well if she had enough speed to back it up!" he mumbles as he sneaks a cupcake with a hair in onto her desk for her birthday. "Kaminari-shounen is so kind and soft! His electric quirk might work better with more power reserves!" he hums, slipping a hair into a brainfried-Denki's mouth on their way to Recovery Girl.
He doesn't really keep track, so he ends up adopting all of 1-A and the big 3. The only reason he hasn't done anything to 1-B is because their actually warier and a little bit saner than 1-A, so he wouldn't get away with it. The only reason he hasn't got to any other classes is because he's either not been introduced, so can't try anything, or those classes are, weirdly enough, entirely sane, so he'd be caught much more easily.
Tho not Mineta. He looks at Mineta, goes "he seems... Enthusiastic!!?!" And sidles away to beg Nezu to get him away from his "more impressionable" kids.
Aizawa still notices, though.
All Might becomes the entire reason the dorms are set up: if All Might is ready to "adopt via quirk-giving", he is going to Parent everyone he gave his Quirk to.
This means the Big Three end up as Dorm Student Heads, but because there are no 2-B students because of Aizawa, the next big three get put in charge of 2-B. 2-B is slightly salty of this fact.
Then Inko meets everyone when they're moving in, then ACTUALLY MANAGES TO CONTROL ALL MIGHT WHEN HE'S FUSSING OVER EVERYONE, AND AIZAWA IS IN AWE, EVEN AS SHE FORCES HIM INTO HIS DORM ROOM AND MAKES HIM SLEEP, BECAUSE SHE IS A QUEEN!
Nighteye goes to visit her with Nezu when told she managed to wrangle Yagi into some semblance of decency and got Aizawa to sleep properly in a bed, so two days later, she's been made Dorm Matron.
Okie, so you know I said about how feral Izuku can be? Yeah, Mineta somehow manages to steal one of Inko's bras (she's a MILF, her room is on the ground floor guarding the Girl's dorm, she leaves her door open should anyone need to hide in there to calm down for a bit. Mineta takes advantage of that.) Izuku nerfs him, then drags him right up to Aizawa like "EXPEL THE PERV!!" (And the only reason Bakugo doesn't do a murder is Iida and Kirishima holding him back.)
For Mineta's safety, Mineta is moved to Gen Ed. Because he's one of the qualifiers in the last game and Aizawa's student/son, Shinso Hitoshi takes his place!!!.... After a decontamination unit has finished cleaning what was Mineta's room so there is no sign of that slimeball left in there.
It is at this point that Izuku figures out what All Might's done when All Might, inevitably, "adopts" Hitoshi. Izuku confronts All Might and All Might is like "yeeaaahh..."
And Izuku doesn't lose his shit, instead he starts jumping around like a rabbit-pupper-floofball going "THAT EXPLAINS SO MUCH!" and "ICAN TEST SO MANY HYPOTHESES NOW!"
At this point Summer Camp happens.
Everyone finds out the sheer feralness of a bunch of suped-up Teens who have had their family threatened.