Gearshift

Gearshift originated with Toshitsugu Kudo and rode inside One For All through generations of successors before reaching Izuku Midoriya. That company transformed it: what began as a trick for nudging small objects ended as a power capable of bending physics, punishing enough that Izuku reserves it for emergencies.

It ranks among the oldest abilities on record. The others of that vintage are Fa Jin, Spearlike Bones, Life Force, the unnamed Luminescence power, and the twin pillars of All For One and One For All. Gearshift no longer exists, destroyed during the Final War in the act of being handed to Tomura Shigaraki.

The power alters how fast something accelerates through space, and it does so without regard for inertia. Contact serves as the trigger, after which the effect rides on whatever was touched, be that a loose object, another person, or the user's own body. The anime renders it as a blue glow sheathing the target, with living subjects' eyes lighting up to match.

Kudo's version was narrow. Only small things responded, and All For One dismissed it as little more than a peashooter. Melding with One For All changed that entirely. Evolved alongside the core power, it came to accelerate a full human body hard enough to trail a sonic boom and land with crushing force. Its scope broadened to targets of every kind and reached as far inward as individual cells, and paired with One For All's raw might it warps the laws of reality outright.

That growth arrived with a price steep enough to designate the power a last resort. Kudo warned Izuku that five minutes was the ceiling before the effects incapacitated him. Held open too long, the ability starves the body of oxygen and leaves Izuku unable to breathe properly. Every use past that first window doubles the previous blowback, driving intense pain through the body and leaving the user close to paralyzed. Because it remained a distinct Quirk Factor inherited from its original owner, All For One could strip it away once Tomura had surpassed One For All's will, and it could also be transferred deliberately. Passing it along during its recovery period drags the recoil with it, as Tomura found out.

Kudo built his fighting around gauntlets mounted on his arms, adjusting the speed and trajectory of the bullets he fired from them. His control held up even while All For One had him by the throat, though the Villain never treated him as a genuine threat.

Izuku's first application ran the power through his existing Ultimate Moves, breaking the sound barrier and hitting Tomura hard enough that the noise arrived late. All For One registered the jump in speed and force from their previous encounter immediately. Stacking it with Fa Jin produces Overdrive, output described as 120 percent of One For All and applicable to moves he already knows. Transmission chains punches together, each one shifting the target into a higher gear. Detroit Smash: Quintuple packs five Detroit Smashes into rapid succession.

Late in the war, Izuku spends it on Katsuki Bakugo, whose own Cluster technique combines with the acceleration to launch him fast enough to pull All Might out of certain death. He turns it on himself once more knowing immobility waits on the other side. With the recoil paralyzing his breathing, Izuku and the vestiges settle on transferring the power into Tomura to destroy his mental soul. Blackwhip hauls his failing body into position, the handoff through blood contact succeeds, and the ability is destroyed in the process, dumping its blowback onto Tomura as it goes.

The cellular damage it inflicts on Izuku recalls the degeneration Nine suffered each time he used Weather Manipulation. Overclock invites a closer comparison, since it accelerates perception by stimulating the brain rather than altering physical motion, yet Gearshift may reach brain cells as well, which would explain Izuku acting and reacting while moving too fast to be seen. Both also impose a mandatory cool-down, ten seconds against Gearshift's five minutes, for the same reason: no body holds that much power open for long.