Why Didn’t Decay Kill Aizawa?


In episode 9 of season 6 of My Hero Academia, we saw that Shota Aizawa was able to find a way to counter the effects of the Quirk-erasing bullet by cutting off his own leg to stop the spread of the effects of the bullet. However, Tomura Shigaraki used this opportunity to attack him as he knew that getting rid of Eraser Head would allow him to use his Quirks again. He was even able to touch Aizawa’s face with all five of his fingers, which should have activated Decay. So, if that’s the case, why didn’t Decay kill Aizawa?

Decay didn’t kill Aizawa because it was yet to activate when Shigaraki touched Eraser Head’s face with all five of his fingers. That’s because Aizawa’s Erasure Quirk was still active at the time when Shigaraki touched his face. And before Decay could activate, Shoto Todoroki attacked Shigaraki.

Had Todoroki been a split second too late, Decay would have surely activated and killed Aizawa the moment he lost his concentration when the Shigaraki attacked his face. It was the perfect timing for Todoroki in that very instant because Shigaraki would have surely killed Eraser Head had it not been for his appearance. So, with that said, let’s look at this topic in greater detail.

How Does Decay Work?

Ever since the introduction of Tomura Shigaraki into the My Hero Academia storyline, it was already clear that he was one of the most dangerous villains in the world due to his Quirk, which is Decay. Before Shigaraki even reawakened Decay and inherited All For One from All For One, he was already a very dangerous opponent because his Quirk could kill people almost instantly. But how exactly does Decay work in My Hero Academia?

Even though Decay is Tomura’s original Quirk, it took a while for him to truly understand what it can do and how it actually works. Originally, he believed that its uses were limited to close-range effects as he needed to actually be within striking distance for it to work. That’s because Decay required Shigaraki to touch his target with all five of his fingers for it to work.


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Once all five of his fingers touch Shigaraki’s target, Decay activates and begins to disintegrate it until nothing is left but dust. In that regard, Decay basically decays the object, regardless of whether it is organic or not. This disintegration spreads rather quickly throughout the target’s entire body but begins in the area touched by all five fingers. That means that the only way for a person to stop its effects is to amputate the area affected by Decay before it spreads to the rest of the body.

However, during the battle against Re-Destro, Shigaraki was able to reawaken his Quirk. What that means is that he was able to make use of Decay in its original form when he first awakened it when he was just five years old. Back then, he killed his entire family and destroyed his house without even touching them, as all he did was touch the ground for Decay to work.


As such, Decay was always strong enough to spread from one area to another and decay anything that was connected to the area that Shigaraki touched. This ability was merely locked due to the layers of trauma that Shigaraki unknowingly developed after he accidentally killed his entire family. But in the fight against Re-Destro, he reawakened the original capabilities of Decay and destroyed Re-Destro’s legs by merely touching the ground.

In that regard, as long as someone or something is touching the floor or any solid object while Shigaraki is touching the floor with all five of his fingers, the effects of Decay will spread and kill whoever or whatever is touching the floor. This was what happened when Shigaraki destroyed Jaku Hospital and a third of Jaku City the moment he woke up after he underwent physical enhancements.

Shigaraki also developed the ability to choose things that his Decay would not affect, as that was what happened when some of the Nomus that were in Jaku Hospital were able to survive the effects of Decay. He said that he didn’t allow his Quirk to kill the Nomus on purpose.

Why Didn’t Decay Kill Aizawa?

Back in episode 8 of My Hero Academia season 6, we saw that the pro heroes were able to stand their ground against Tomura Shigaraki because of the fact that Shota Aizawa was using his Erasure Quirk to erase all of the villain’s own Quirks. Nevertheless, Shigaraki’s enhanced body allowed him to fight Endeavor, Ryukyu, and Gran Torino on par, all while Eraser Head kept his focus on him to keep him from activating his Quirks.

But Shigaraki understood that the MVP of that battle was none other than Aizawa, who he needed to deal with first if he wanted to regain the use of his Quirks. As such, the villain proceeded to attack Eraser Head first as the pro heroes struggled to stop him. Shigaraki was able to fire a Quirk-erasing bullet that hit Aizawa’s leg.


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While Aizawa’s Quirk survived when he amputated his own leg before the effects of the Quirk-erasing bullet could spread throughout his entire body, Shigaraki used this as an opportunity to attack Eraser Head. He said that Aizawa lost concentration the moment that he cut his leg off, and that allowed Shigaraki to use his enhanced strength and speed to quickly rush toward the pro hero.

That was when he was able to touch Aizawa’s face with all five of his fingers. But before Shigaraki could kill Aizawa, Shoto Todoroki arrived to blast him with his ice Quirk. Eraser Head was still alive but quickly fell unconscious as the other pro heroes tended to him. With Eraser Head out of commission, Shigaraki regained the use of his Quirks. 

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But the one thing that bothered people was the fact that Eraser Head didn’t die the moment all five of Shigaraki’s fingers touched his face. So, why didn’t Decay kill Aizawa when Shigaraki touched his face?

Well, in that scene, Aizawa’s Erasure was still active. Erasure works as long as Aizawa’s eyes are open and he is looking at one of the target’s body parts. The moment when Shigaraki attacked Eraser Head, Erasure was still in effect. 

As such, it was only when Shigaraki touched Aizawa’s face that the Quirk was disengaged. Shigaraki scratched Eraser Head’s face with his superhuman strength to injure him and cause damage enough to knock him out. As such, the moment that Aizawa was knocked out, that was when the effects of Erasure were no longer active.

Luckily, there was enough delay between the time that Erasure disengaged and the time that Decay could be used again. It was at this split moment that Todoroki arrived to save his teacher from the villain. Shigaraki was just about to activate Decay after he knocked Aizawa out, but Todoroki prevented him from doing so.

In that regard, it was clear that Aizawa was about to die at that moment. Had Todoroki been a split second too late, Eraser Head would have surely succumbed to the effects of Decay and perished right then and there.

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