Power Stock

Power Stock is an Emitter Meta Ability with internal range, counted among the Quirks of One For All. Its earliest holder is unidentified; All For One stole it from that person before passing it to Yoichi Shigaraki. It debuts in Chapter 59 and in Episode 33. The ability hoards power, letting its bearer release it in overwhelming bursts of strength and speed. How the hoarding works was never spelled out, though training and steady accumulation appear to be the mechanism, and All For One rated it gentle enough for even a frail body to bear.

The gift was a manipulation. All For One handed the ability to a brother he took for Quirkless, betting that power Yoichi had never known would pull him into the reign of terror. Neither man knew Yoichi already had a Quirk, one whose only capability was being passed to someone else: Quirk Bestowal. An incomplete Quirk Factor, a product of his upbringing, had left that power short, and Power Stock supplied precisely what was missing, so the pair merged and became One For All.

The merger let the ability outgrow anything it once was, since each transfer cultivated the reserve further and compounded it down the line. By the eighth holder, Toshinori Yagi, the hoard was vast enough to make All Might the strongest man alive, strength he spent dismantling the forces of All For One and finally the man himself, at severe cost to his own body. By the ninth, Izuku Midoriya, it had crossed a tipping point, forcing him to train himself to meter it out or wreck his own limbs. He began at only 5 percent, since more would maim whichever limb released it, climbed to a ceiling of 45 percent, and leaned on the other Quirks lodged inside the ability to hit what amounted to a safe 100 percent. His body later toughened enough to run at a true 100 percent with far less harm, and threading the power through Gearshift and Fa Jin in the Ultimate Move Overdrive pushed him to 120 percent.

The lineage runs from an unknown original holder through All For One, listed as a former user, to Yoichi Shigaraki, and onward down the chain of One For All bearers that takes in All Might and Izuku Midoriya. Tomura Shigaraki ends it. Forced to take One For All during his final battle with Izuku, he inherited an ability already past its tipping point, and it was destroyed almost immediately. The massed power of every earlier holder proved more than his body could endure: he began deteriorating, Super Regeneration could no longer mend him, and one decisive blow crumbled him.

Power Stock also ranks among the series' oldest Quirks, alongside Luminescence, Spearlike Bones, Gearshift, Fa Jin and Life Force, plus the three intertwined powers at the story's centre: Quirk Bestowal, One For All, and its dark counterpart All For One. It shares a name and a broad effect with Power, which delivers great strength with no stockpiling required.