Work Text:
There's a poem thingy that the loss of a single nail lost the shoe which lost the horse which lost the rider which lost the message which lost the battle which lost the kingdom all because of a horseshoe nail.
So in this fic, the loss of one single nail changes everything.
The nail?
All for One.
In this universe, he never became a villain.
Zen and Yoichi are good brothers who are also immortal because Zen got quirks for them to live together forever and Yoichi still has One for All, although he didn't know it could be transferred because he never tried to with no reason to. The brothers briefly toyed with the idea of being heroes, but there was a lot of discrimination against quirked people back when they were still living their first lifetime so they went underground for a bit, taking new identities whenever their old ones should've died by normal rate of aging.
When they came back out, society was still settling down and the two of them tried to as well. When they were finally settled and heroes were commonplace, the Hero Commission was kind of corrupt already and Yoichi and Zen decided they didn't want anything to do with them.
Although sometimes they act as minor vigilantes, but nothing large enough to get on anyone's radar. Just helping out the little guy here and there.
The butterfly effect comes in later. There's no League of Villains, no Nine, the Shimuras are still alive and Nana never left Kotaro so they're all stable and nice people. Also Tenko might not have been born because I think I read somewhere that Zen was the one who convinced the family to have another child.
There's no One for All, and even if Nana Shimura met All Might, he's still quirkless. Even if he's still a hero, he never became All Might, a shining beacon comforting the populace and taking down villains.
So by the time present day rolls around villains are still a major threat and it's dark days for Japan. But at least Endeavor's not abusive... although he might not have married Rei at all so the Todoroki kids don't exist.
Oh, and it's dad for one, because Zen fell in love with a certain Inko Midoriya/Shimura if you subscribe to that theory. Izuku Shigaraki inherits All for One and he's creepily smart with his quirk analysis. And if you really want to make Izuku overpowered, imagine what All for One mixed with Inko's attraction quirk could do. Izuku could steal quirks at a distance and no one can stop him.
Bakugo and Tsubasa, the winged kid who's also the grandson of the doctor who diagnosed Izuku, are his best friends. They're kind of a trio, even if the trio consists of angry kid, creepy kid, and more or less normal kid who tells them when they're being crazy. They're the only ones outside of Izuku's immediate family who know what Izuku's real quirk is.
Izuku's passing off his quirk as regeneration, because Zen is a bit overprotective and made sure all of his family members got copies of the best regeneration quirk he could find just in case something bad happened to them. Izuku also convinced him to lend some to his friends and their parents. Mitsuki and Masaru know because they're close with Inko and Tsubasa's parents are Garaki's kids so...
Izuku's not immortal yet, because Inko said that immortality was a decision he'd have to make for himself when he's around twenty five. Consent and all that.
Since canon is completely derailed, the story idea was to make it mostly pre-canon and in middle school. Izuku dealing with normal middle school stuff in a dark age with villains around causing chaos.
Oh, and because Izuku is a danger magnet, he runs into Eri and rescues her while his parents and uncle systematically destroy a yakuza. Izuku may or may not have stolen Overhaul's quirk.
And Izuku, testing out a hacking quirk, breaks into the Hero Commission's servers and reveals how corrupt they are to save Hawks and Lady Nagant. Typical teenage stuff.
The fic was going to end with Izuku getting his letter back from the UA entrance exam and a line about how Izuku was going to be a hero, but you do you I guess. I'm not writing this anymore.