My Hero Academia is chock full of terrifying and exemplary villains who really give the heroes a run for their money. But few can hold a candle to the leader of the League of Villains himself, Tomura Shigaraki. In addition to his ideals, part of what makes him a worthy adversary to the series' protagonist, Izuku Midoriya, is Tomura's destructive Quirk known as Decay.
Decay allows Tomura to disintegrate anything he touches with all five fingers, living or not, and he is hellbent on exploiting his Quirk's deadly capabilities for his own purposes. With the My Villain Academia arc now reaching its climax, Tomura is forced to face his limitations as his growth is thrust into the spotlight. Here are five lesser-known details about Decay.
5) Shigaraki's Decay Quirk Was Born of a Rare Mutation
Quirks in My Hero Academia typically manifest in a child anytime from birth to the age of four, and whatever extraordinary powers develop are genetically inherited. A child can manifest their mother or father's Quirk (e.g. Kyoka Jiro who has her mother's Quirk, Earphone Jack) or a combination of the two to create a similar, yet new ability (Katsuki Bakugo's Explosion). Quirks grow stronger as they evolve with each new generation, but it's easy to see where they come from. However, Decay does not follow these rules. It is an extremely rare mutation, meaning it developed naturally outside of genetics, thus not much is known about this branch of Quirks.
The only other MHA character to have a rare mutation Quirk is Eri, and as such her backstory draws many similarities with Tomura's. When Decay manifested, it went out of control and Tomura murdered his family. Eri's Quirk, Rewind, reverses a living body back to a previous state. Rewind also went out of control upon manifestation as Eri unintentionally murdered her father. Both families were confused and horrified at the revelation and both children were left alone. Tomura had no more family while Eri's mother gave her up. They both also ended up in the hands of villains.
4) Tomura Shigaraki's Quirk Is Reminiscent of Overhaul's Quirk
A unique ability to turn anyone or anything to dust, Tomura's Decay has several similarities to Overhaul's Quirk, fittingly known as Overhaul, which can deconstruct and reconstruct anything he touches. For starters, Tomura can only destroy and cannot control Decay spreading throughout an entire object or body. On the other hand, Overhaul can reassemble the damage he inflicts and has full control over how much he destroys and repairs.
But Tomura is not without his merits. Originally he needed all five fingers to activate his Quirk whereas Overhaul only needed one. During the My Villain Academia arc, however, Tomura unlocks the true potential of Decay thanks to recovering his memories and the intense training with Gigantomachia. Now, Decay affects anyone and anything connected to whatever Tomura is touching, turning them into dust within seconds and becoming a crucial weapon against the Meta Liberation Army. Upon proving his ideals and determination, this strength allows Tomura to best the MLA just as he did Overhaul long ago.
3) Shigaraki's Quirk Is Somehow Resistant to Gloves
As mentioned, Tomura's Quirk is purely destruction with no ability to fix what has been disintegrated. While this power is an instrumental tool for killing, it also leaves no room for error. This poses the challenge of how to touch things or people without accidentally disintegrating what he doesn't intend to. In the past, we've seen Tomura taunt his enemies with only four fingers -- like he did to Izuku back in MHA Season 2, threatening to end his life by almost placing all five fingers around his neck. But recent flashbacks have shown Tomura's Quirk staying dormant -- even when wrapped in a full pair of gloves.
Despite all five fingers touching the fabric, the gloves do not disintegrate -- which goes against the rules of his Quirk. What makes this detail even more confusing is that this takes place shortly after Decay manifested and was too powerful for Tomura to control. Artist gloves would make more sense since they cover two fingers and leave the rest bare. In My Hero Academia: Heroes Rising, Tomura is able to use Decay against Nine with only two fingers, but since the second MHA film takes place after the Paranormal Liberation Front is established, this may be a result of his growth.
2) Tomura's Tendency to Scratch Himself Is Likely Due to His Quirk
Ever since Tomura's introduction in My Hero Academia, fans have been quick to raise questions as to why he's always scratching himself and why his skin is so dry. Many think he could have eczema, a medical condition where the skin becomes inflamed and irritated. While Tomura's condition may be reminiscent of eczema, the canon explanation is because of his Quirk. Thought to be allergies, Tomura's flare-ups are actually a result of Decay likely irritating the skin from the inside out. This is plausible as Quirks can commonly alter a person's physical traits.
What causes Tomura to itch are negative emotions. Whether it be fear, bloodlust or frustration, Tomura is always in a foul mood when the itch returns and it's intensified by how strongly he feels these emotions. In addition to being a physical attribute of Decay, Tomura's psychological state plays a huge role in his scratching.
1) Tomura Shigaraki's Mental State Is Crucial for His Quirk
Taking the connection between Tomura's psychological state and his Quirk a step further, the limitations and progression of his abilities seem strongly influenced by his emotions. Decay first manifested under intense negative feelings and quickly proved to be a power too strong for Tomura to wield as a four-year-old. However, shortly after he is taken in by All for One, Tomura's memories are suppressed and with it, the true extent of his Quirk. Despite losing those memories, he continues to wear the hands of his dead family members as a constant fuel for his bloodlust.
When Tomura's memories begin to resurface against the MLA in recent My Hero Academia episodes, so does Decay's true power. The difference now is that he's trained his body intensely as he overcomes his past to push forward in his quest to tear down society.