Warning! Spoilers ahead for My Hero Academia chapter 339!

As the cast of My Hero Academia heads towards their final confrontation with All For One, Deku will not fight at full capacity, and it's all thanks to Mei Hatsume - and to a lesser extent Principal Nezu.

Deku and Tenya Ida recently visited U.A. High's master gadget-maker Mei Hatsume to repair their hero costumes. Both of them, not an enemy, damaged each other's suites when Tenya and his classmates had no choice but to use force against Deku when he decided to face All For One alone. Fixing them was a high priority since the two heroes in training just received a new mission that is currently undisclosed to the reader, which somehow involves leveraging the traitor Yuga Aoyama to their advantage. But in chapter 339, Mei originally flat-out refuses to fix them but eventually provides some cheap knockoffs that she made with her non-dominant hand while talking with them.

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Unfortunately for Deku and Ida, Mei has more pressing matters than their costumes. Many chapters ago, Principal Nezu revealed to class 1-A all of the upgrades U.A. High received to protect everyone sheltering there. Power Loader was assigned to the project because he recently recruited Mei to help improve Nezu's evac shelter blocks. Based on the layout design Mei shows Deku and Ida, the project basically involves installing some sort of propulsion device to certain sections of U.A. High that have been separated into blocks. The propulsion system is meant to move these blocks to safety during an evacuation.

In actuality, Mei had already finished the project but is continuously looking for ways to improve her designs. Putting aside time to repair Deku and Tenya's costumes could negatively affect the evac shelter blocks, which essentially turn U.A. High into a robot. However, she doesn't just leave Deku and Tenya hanging. While explaining her mindset to them, she builds knock-off designs. In addition to proving her dedication and skill, her failure to help Deku will force him to become more like All Might. What needed repairing were parts she initially created to help Deku deal with the blowback he sustains when summoning One For All. Specifically, her iron soles and air force gloves protected his feet and hands respectively.

Before Mei made his soles and gloves, Deku couldn't unleash One For All without hurting himself. For wielding the quirk in his hands, he acclimated by limiting blasts to each finger, which he achieved by flicking. The finger he used to flick automatically sustained a massive injury. Although he would lose the use of a finger, focusing the power allowed him to unleash One For All 10 times instead of just two if he used his whole hand. Mei's gloves allowed him to wield One For All without breaking his fingers.

Meanwhile, All Might never needed a special costume to use One For All without hurting himself. As the inheritor of One For All, Deku was destined to become the next All Might, but the fact that he couldn't even accomplish what All Might could do naturally put him at a disadvantage. Luckily, Deku was born quirkless because it made him inherently more suitable for wielding all of the quirks of One For All's predecessors. All Might was also born quirkless, but One For All's power hadn't developed enough for him to wield these additional quirks at the time. So even though Deku has fewer protections, this will force him to learn how to lessen the damage he sustains from wielding the quirk, making him even more like All Might before his retirement in My Hero Academia. But because he can now wield more quirks than All Might could, Deku's lack of protection will push him even farther ahead of his teacher and hero.

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