Gearshift

Gearshift was the Meta Ability used by the Second User of One For All and later inherited by Izuku Midoriya.

Description
Gearshift allows the user to change the speed at which things accelerate through space.

Weaknesses
According to the Second User of One For All, Gearshift has evolved into an unusual power since melding with One For All that cannot be wielded the usual way, thus has been designated as a last resort. Not much is known about these setbacks, but the Second User has told Izuku that once he used the Quirk, he would only have five minutes to finish the job, implying the strain of using the power will take him out of the fight after time is up.

Usage
Not much is known about Gearshift when used by the Second User, but he has implied that the Meta Ability has been greatly enhanced by One For All.

Izuku first used the Quirk to make all of his Ultimate Moves faster to the point where he broke the sound barrier, inflicting heavy damage to "Tomura Shigaraki" as the sound was delayed before it can be heard. All For One through Tomura was able to recognize the significant increase in speed and power from their original encounter.

Trivia

 * Gearshift is one of the oldest known Quirks in the series along with One For All, All For One, Life Force, Spearlike Bones, Fa Jin, and the unnamed Luminescence Quirk.