My Hero Academia's manga is continuing the build-up to the next big event, which will be the Meta Liberation War. That conflict has the radical Meta Liberation Army teaming with the League of Villains, in order to destroy all of society's laws and rules about restricting quirk use. In order to prepare for the oncoming battle, Japan's Pro Heroes are drafting the exceptional students of U.A. Class 1-A into their forces, by trying to boost their respective quirks to new heights of power. In that spirit, All Might has just provided Izuku Midoriya some crucial information about his One For All quirk, and how that power was passed down from various users all the way to Deku.
Warning: My Hero Academia manga chapter 257 SPOILERS Follow!
The key revelation in My Hero Academia chapter 257 is All Might telling Deku and Bakugo that the previous holders of One For All weren't quite the same as Deku and All Might himself. The previous holders like Daigoro Banjo / Blackwhip or Nana Shimura all received One For All as a sort of survival mechanism built into the quirk, and that limited their ability to access its power. It's revealed that All For One has always hunted down and killed All For One users, and that each time those users managed to pass on One For All to the nearest recipient, just before their respective deaths:
"All For One was obsessed with One For All," All Might explains. It was an age when evil wielded a degree of power that's hard for us to imagine nowadays. All For One went around crushing the strong, because there was nobody who could defy his sheer malice and control. Writing in that Hellscape, as they lay down to die, the past users made sure the power would reach the future. They weren't really chosen ones. Through all those battles, all they could do was receive the quirk and entrust it to another."
The full details have yet to be explained, but the premise here seems to be that choosing someone to inherit One For All has a significantly different effect than simply passing it one as means of the quirk's survival. It helps to explain why All Might and Deku are such unique standouts in the hero world, with there immeasurable smash powers, while other previous One For All users never achieved notoriety at all (their quirks weren't powerful enough to make them standout heroes). It's both a nice plot-hole filler and a way of distinguishing All Might and Deku as being extra special cases in the long line of One For All users.
My Hero Academia was created by Kohei Horikoshi and has been running in Shueisha's Weekly Shonen Jump since July 2014. The story follows Izuku Midoriya, who lives in a world where everyone has powers, even though he was born without them. Dreaming to become a superhero anyway, he's eventually scouted by the world's best hero All Might and enrolls in a school for professional heroes.