Yet another Reddit post that I'm throwing onto here!
The Wrong Quirk
(Inspired by N/A)
Okay, so here's the basis for my idea of a possible Villain!Deku fic:
What if the quirks were swapped around? What if instead of All Might having One for All, he instead has All for One, and gives that to Izuku?
So here's how I imagine this going: At some point in the past, One for All and All for One did a switcheroo. Somewhere along the line, the original All for One bit the dust, but his quirk lived on, and in a twist of fate, All for One was misremembered as the heroic quirk of the duo that was passed down from person to person, and One for All was the evil one, and so it's All for One that is passed down from person to person instead.
Only problem is that, well, we all know what happened to Shigaraki in canon, and how he was hijacked by the OG All for One, so instead of Izuku having this cool quirk that has been passed down from person to person, he instead has this ticking time bomb with the original AFO's consciousness inside of it, slowly biding his time and regaining his strength to hijack and take over the minds of not just Izuku, but also All Might, and anyone else who is currently using All for One...
Hell, if we want, we can take it even further by having the League of Villains being controlled by someone wielding One for All, only this time it's the League who are the good guys in this story, as they're the only ones who know what All for One truly is and are trying to stop him before it's too late, essentially turning the League from a rabble of anarchists to a heroic resistance.