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Quirks in My Hero Academia can easily make or break a hero or villain. The quirk certain characters are born with can even affect what path they follow in life. Particularly, people born with dangerous or evil-seeming quirks seem destined for a life of crime, even if they might not originally want that for themselves.

Such was the case for a young Tomura Shigaraki, who dreamed of being a hero, but eventually grew to be the main antagonist of the series. All because of the dangerous quirk he was born with. As he got older, Shigaraki's quirk has become more complex and even more dangerous. So just how does this devastating ability work?

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Basics

Shigaraki Tomura in My Hero Academia

Shigaraki’s quirk is known simply as ‘decay’. As the name implies, it is a quirk that allows its user to decay or destroy anything that they lay their hands on. The speed and ferocity at which the quirk decays things is dependent on the user’s emotional state, with strong, chaotic emotions causing the quirk to act more fiercely. The decay effect has been shown most often to reduce its targets to dust, but has also been shown to be able to reduce living targets to a pile of blood and body parts in its weaker form.

Evolution

Shigaraki from My Hero Academia

Decay is an interesting quirk due to the way it changes over the course of Shigaraki’s life. It’s less that the quirk evolves or that he learns new ways to use it, and more that he simply remembers its full potential and chooses how much of it to tap into at any given time.

When he was just 5 years old, Shigaraki first manifested the quirk, killing his dog in the process. He then accidentally decayed his sister, causing him to panic and his quirk to go out of control and start decaying his family’s backyard. Before long, the decay effect spread and killed his other family members, despite him never touching them. Ultimately, fueled by rage against his father, the quirk ended up demolishing the family’s home completely.

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For years after this, Shigarai’s trauma caused the quirk to regress to a weaker state, where it would only activate if he placed 5 fingers on his target at once, and the decay effect was rather slow. For example, when used against Eraser Head, decay only broke down some of the skin on his elbow, despite Shigarki having a hold of him for a few seconds.. This is the state decay is in at the start of the series.

After the events of the ‘league of villains' battle against the ‘meta liberation army’, Shigarki recalls his childhood, and is able to return his quirk to its former state. In this state, it can spread from object to object, doesn’t require all 5 fingers to activate, and can also be activated using Shigaraki’s feet.

Limitations

My Hero Academia decay quirk shigaraki

Besides the trauma-induced limitation the quirk had earlier in the series, decay is actually lacking in many major weaknesses. Once Shigaraki fully restores it, it becomes a quirk capable of effortless mass destruction.

However, it is shown that using it can damage Shigaraki himself, as it severely damages his arm when he unleashes it in order to defeat Re Destro. Even in its strongest form though, the quirk does still require physical contact, so if Shigaraki is suspended in mid air for any reason, his quirk becomes completely useless, and he is much easier to defeat. Similar to Overhaul, his quirk is also locked to certain limbs, so if his fingers and toes were cut off, he wouldn't be able to use the quirk anymore.

Achievements

Tomura Shigaraki With Broken Arm Standing Among Rubble

The day it first manifested, decay showed itself to be capable of leveling a house in a few minutes. Once an adult Shigaraki restored its true power it reached even greater heights, being able to level entire cities in a few moments, decaying anything that happened to be in the vicinity.

The quirk also shows an element of precision, with Shigaraki being able to control what the decay spreads to. It’s unclear how precise this selection is, but it could potentially mean he can selectively decimate an entire battlefield, while keeping his allies alive. It's a quirk so powerful that even One For All.

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