One For All: Full Cowl - 100% (ワン・フォー・オール フルカウル 100%パーセント Wan Fō Ōru Furu Kauru 100 Pāsento?, Viz as: One For All: Full Cowling - 100 Percent) is a variation of One For All: Full Cowl that Izuku Midoriya and Katsuki Bakugo use to maintain One For All at 100% full power.
During the final battle against Overhaul, Izuku unknowingly went over his personal limit because Eri's Quirk undid the damage to his body before he ever felt any pain. This allowed Izuku to get a feel for how quickly his body gets rewound by Eri.
Using Eri's power to negate the backlash from overusing One For All, Izuku can draw out the maximum power his Quirk has to offer. 
Full Cowl at 100% dramatically increases all of Izuku's abilities, granting him strength and speed that rival that of All Might, and the ability to move through mid-air using wind pressure.
At infinite 100%, Izuku completely outmatched Overhaul in his final form. He was able to launch Overhaul's massive form into the sky with a single kick before beating him down with continuous punches that prevented the villain from healing himself.
In this form, Izuku's hair stands up, gaining a spiky appearance, while glowing a brighter shade of green than normal, and yellow (blue in the anime) energy flows from his eyes with his electricity being blue instead of the usual green. His skin also adopts a reddish hue. In both My Hero Academia: Heroes: Rising and the manga, his pupils and irises become distorted.
When Katsuki Bakugo temporarily received One For All, he gained the same level of physically altered feats at Izuku, albeit with a few differences: his hair became spikier, while glowing a brighter shade of yellow, and the emitted electricity was orange. While using One For All Infinite 100%, Katsuki not only gained similarly enhanced physical strength and speed as Izuku, but his Explosion Quirk became potent enough to instantly melt through solid rock, in a manner similar to lava, as he came into close proximity of it. Using this technique along with Izuku, he was able to defeat Nine in his powered-up state, who ended up being completely incapacitated after the fight.
When Izuku first used this technique, the major drawback of was that Eri is unable to control her Rewind Quirk as of yet, and therefore, her ability to maintain Izuku's form becomes unstable. It is likely Izuku could have been killed had it not been for the intervention of Eraser Head. During the final battle with Nine, however, Izuku and Katsuki were able to access this technique unaided, and without their bodies being blown apart from not fully mastering One For All. This may have been due to their exposure to Katsuma Shimano's Cell Activation Quirk, which was stated to boost the body's physical condition.
- ↑ My Hero Academia Manga and Anime: Chapter 157 and Episode 76.
- ↑ My Hero Academia Manga and Anime: Chapter 158 and Episode 76.
- ↑ My Hero Academia: Heroes: Rising.
- ↑ My Hero Academia Manga: Chapter 159.