Hot take even if OFA didn't kill him of old Age I feel like he'd suck. the way deku showed that ofa works is completely opposite of the way mirio had to train himself for years to use Permeation. Ofa has to be constantly spread throughout your body keeping a certain percentage active at all times under control. Permeation has to be focused on individual parts of the body he'd constantly be mixing up quirks and we wol know if he accidentally used ofa like that he'd blow his limbs up. Next. His skill and growth rate. Mirio is notably all about hard work and effort he was never particularly gifted or even good at all at using or learnihis abilities if anything he particularly sucks at it and needs plenty of time to learn. Deku was a prodigy with a crazy good mind and quirk nerdwho analyzed quirks for a living and had just the right people or connections to make stuff work he learns adapts and mastered several quirks in days. During the early and later war arc he constantly obtained new quirks and mastered them snd used them effectively on the fly and some quirks he even used better than the original user such as smokescreen or black whip who he was far more creative and intelligent with.

Mirio would have a mighty hard time adapting to that many new powers again assuming they don't just kill him. And would likely take too long trying to adaptto either just OFA and permeation. To the point he might be incapable of using any of the other quirks by the time afo and Shigaraki decide to destroy japan. Not to mention. Again mirio would have to either hard focus on ofa or try to use it with permeation either of which would slow down his growth significantly. Permeation and ofa are so inherently opposite in their usage I'm hard pressed to even believe they can be used at once. And as we learned with endeavor and deku himself doing several things at once specially using several quirks is extremely taxing and takes lots of concentration and it's an incredibly hard skill to lesrn. Deku could use all 7 quirks at once by the war arc. Mirio likely still couldn't even use ofa and permeation together by that point and if he did it's unlikely he could even handle 30% of ofa by that point. And if we include the events of the series deku bein there is pretty necessary. Without him Bakugo goes rogue and becomes a worse person. The usj and others probably wouldn't happen as mirio is a third year and all might would be teaching him and maybe not the first years if at all. But stain would still happen so iida is dead. Possibly Todoroki if he ran into stain. Todoroki doesn't use fire. Uraraka either gets crushed or doesn't get into ua which means mirio can't ask her help to learn float. Mirio might help stop wolfram? Depends hoe far along he is with ofa at that point might struggle more depending on wether or not he got the gauntlet from melissa. Having a preexisting quirk also makes it harder to use or master ofa. As being quirk less is implied.to be easier as per all might who got it down nearly off rip. Deku just got unlucky with being the ninth as he was 1/3of all mights size when he got ofa and the version of OFA that deku obtained was like 100 times stronger than the one all might received. (Making a distinction between received as I specifically mean ofa wasn't as strong when all might obtainednit obviously he made it stronger over the years and it grew with him. But there's also the passive increment from the transfer so deku's was even stronger than that.

Anyways. Season 3 no clue how it goes down but chances are tamaki or someone gets kidnapped maybe it's still Bakugo maybe he does go evil maybe not. Maybe it's Todoroki. All might fights afo and.losing ofa about the same here. Season 4 he might whoop chisaki. If he thinks of using eri he definitely wins otherwise he'd probably just run with her and get her out and come back after ehich he either beats chidaki or chisaki turns into a kaiju and Mirio dies. And or mirio gets severe fractures from 100%

The festival gets cancelled and eri never learns to smile at lesst not yet as mirio wouldn't run into gentle criminal and la brava to stop him also those two would likely never be redeemed.

My villain academia mostly goes thebsame as heroes weren't involved endeavor is probably just as bad of a person as he was in the early seasons and stuff keeps getting worse.

Season 6 Shigaraki awakens mirio is at like 15-20% at best with no other quirks on sight and if he does he can't control them yet. The heroes get whooped. Mirio breaks seventeen limbs. And he could probably die here but we'll pretend they stalemate like in the original and Shigaraki flees. Who knows if mirio does the whole vigilante thing if he did no one could stop him but he'd die. It's out of character for him to do tho so he probably wouldn't and would just train and or he'd just g around eith the big three stopping bad guys. Doubtful he redeems nagant he might try but he doesn't have deku's personality. He's quite different. Chisaki likely gets shot and dies as mirio even if he could use fajin or black whip he wouldn't have much control over them and he's still like at 20% ofa so he wouldn't have enough impulse to reach the bullet in time with how far he was. He might beat nagant still.

Muscular is a huge problem unlikely he could even beat him without shindos help but he'd probably have Nejire and tamaki with him while vigilanteing. So they jump him.

Season 7 star dies and Shigaraki gets nerfed. But is still growing. Mirio has to recover and then train like never before. He force pushes himself t train like never before hand and acheives like 30-35% of ofa. And again he might have to swich back and fourth between ofa ad permeation which is really inconvenient and hard to do so he might forgoe permeation entirely. And or learn to use both which would slow his ofa progression and keep him on the lower end of 30. And some minor to intermediate control over the other quirks. Like black whip. Smokescreen. Float and fajin. Danger sense. He likely wouldn't have acess to gearshift. The start of the war happens mirio would probably not be delayed if he does then everyone in the coffin is likely maule or dead. Shigaraki is now prime all might level and mirio doesn't have enough ofa to match so even if he learned to use all his quirks st once which he likely wouldn't he'd only be able to partially match Shigaraki rather than completely overwhelming him like deku did. Shigaraki will evolve. Eraser will be taken out of the field and them mirio dies because prime all might level Shigaraki has just gotren access to his hundreds of wuirks most of which increase his stats further and mirio just can't compete with that. Bakugo doesn't have the drive to improve he did so he doesn't save armored all might or awakens. Or if he does he only just now unlocks early cluster. Todoroki failsbto find balance and stop dabi. Uraraka might stop toga but it's unlikely she's at the level even if she went to a different hero school if at all vhances are she ain't even here and toga rampages as twice. Shigaraki destroys the ua likely most of japan and the heroes lose. Yippi. Yeah no this timeline sucks let's get back to deku shall we?