Full Gauntlet

All Might's raw physical output gave Melissa Shield her design brief. She wanted gear that could survive strength on that scale, and what she built ended up in Izuku Midoriya's hands during his stay on I-Island.

Dormant, the device reads as nothing more than a red band worn at the wrist. A button sits at its center, and pressing it makes the material spread and reshape until it grips the contours of whichever forearm is holding it. Once released, the thing looks less like armor than like a fighter's taped fists, or bandaging wound over a palm and up the arm.

Three strikes at undiluted One For All are what the equipment guarantees, delivered without the shattered bones such output normally costs its bearer.

Below that ceiling the benefit changes shape. The gauntlet steadies whatever percentage Izuku selects, letting him push Full Cowl well past his usual safe margin while keeping hold of the result.

Izuku is the only person shown wearing it. His first trial run came at thirty percent against the drones of the I-Island Security System, and he saved the full hundred for the central tower, punching an opening straight through its wall. The battle that closed out the incident, against Wolfram, wrecked the device for good.

A small footnote to the whole episode is that Izuku never worked out how to get it off and simply kept it on. The Mid-Gauntlet, a weaker relation resting on the same safety principle, is implied to descend from Melissa's design.