He manages it.

Izuku took a deep breath, remembering what All Might told him not to say about One For All. They had agreed to just say he was a very late bloomer, but he realized that cases like that were nonexistent. The majority of Quirks manifested by four, so pushing the idea of his Quirk manifesting at 18 would be an extremely difficult sell under even the slightest scrutiny. And he knew Bakugo would be the first to call bullshit. He needed something way more believable, and fast.

Hiding nearby, All Might, having come to see Izuku's Quirk Assessment was mentally trying to will Izuku to just stick to the story they agreed on. Unaware of this, Izuku started to speak, slowly to try to stall. "It's... Kind of tricky to explain... Because, see, until recently, I didn't even think I HAD a Quirk..."

"You mean you're that late of a bloomer?" Iida asked skeptically.

"Like hell!" Bakugo growled, currently thinking Izuku had hidden it to mock him somehow.

"Actually, no. It DID manifest before now," Izuku stated, surprising everyone.

"What are you doing, Young Midoriya!?" All Might thought frantically, strongly considering going out there to introduce himself as the Heroics Teacher earlier than planned, and claim the reason was because he was unaware that Aizawa tended to skip orientation, and had come looking for Class 1-A when they weren't there, in order to provide a sufficient diversion to make everyone forget the current subject. His fame did tend to have the effect of making people forget everything else going on at the moment.

Before he could follow through on his plan, Izuku continued, his mind racing, and coming up with a cover that bordered on truth, but bent it in many places. What he had said before was actually true: One For All DID manifest long before recent months... Just not in him. "You see, it existed before I discovered it, I just couldn't access it, so for all intents and purposes, until I could, I didn't have a Quirk," Izuku pressed on, gaining confidence in his story.

Seeing Izuku seemed sure of what he was doing, All Might decided to have faith in him. "...I'm just going to, as the youngsters call it these days, let him cook... I hope you know what you're doing, Young Midoriya."

"It basically works by stockpiling power, which I can use to enhance my physical abilities, but until recently, that was all it was doing for me. I had no access to that power. The more time goes on, the more power builds up. I guess you could say it needed to reach a certain point before I could actually start using it," Izuku finished, now actually using a small amount of falsehood, but keeping it to a minimum so as to avoid telling anything obvious, and leaving as few holes as possible. He just needed to make sure no one knew it was a Quirk that was passed on from host to host, while also explaining why he was Quirkless but suddenly had a Quirk.

He was stared at by many classmates, and the pink girl whistled. "Dang, that must have sucked, Quirkless people are treated in unacceptable ways these days. I imagine you got bullied a lot, huh?" she asked, rather bluntly.

"Yeah, you could say that..." Izuku rubbed the back of his head. Putting two and two together, Momo glared daggers at Bakugo, the relationship they seemed to have before clicking. She had embarrassed him before because he was being an ass and seemed to have a grudge against her Master, but she hadn't known for sure it was outright bullying until now... She decided at this moment that she would make it her personal mission to make Bakugo's time in U.A into a living hell. At least until he had suffered at least a good portion of what he must have inflicted on Izuku.

Bakugo wasn't sure why, but he felt a shiver run down his spine... As if getting the odd sense that he had pissed off something he really shouldn't have.

(A/N: Yes, Bakugo, yes you did. Mwahahahahaha...)

All Might meanwhile relaxed significantly. That... Might not have been their plan, but in hindsight, he realized that just saying Izuku was a very late bloomer was just ASKING for way too much scrutiny. The idea of a Quirk manifesting, but simply not in a manner that was easily noticeable until later was much easier to swallow. There probably actually WERE cases of that happening. He was sorry he doubted Izuku in that moment.

Aizawa proceeded to dismiss the class, and noticing that Izuku was moving a little stiffly, sent him to Recovery Girl. After being treated for some minor muscle tears, he headed home, where Momo and Ochaco were waiting.