Decay

Quirk Information
Japanese Name	崩 (ほう) 壊 (かい)
Rōmaji Name	Hōkai
Quirk Description
User	All For One (Formerly) Tomura Shigaraki (Formerly)
Quirk Type	Emitter
Quirk Range	Contact
First Appearance
Manga Debut	Chapter 16
Anime Debut	Episode 11

Decay (崩 (ほう) 壊 (かい) , Hōkai^?) was the Quirk used by Tomura Shigaraki, given to him by All For One.

Description

Decay allowed the user to destroy anything or anyone their hands touch, making the _target crumble to dust.

Tomura uses Decay to kill a Shie Hassaikai member.

Whether the _target was organic or not, Decay would work without fail. As such, this Quirk was extremely lethal against living beings, having their flesh rot away if hit by it. The speed of the disintegration had developed from slow to almost immediate, eventually spreading through the whole body if a victim doesn't amputate the decaying body part (Eraser Head was able to avoid this by erasing Decay before it could cause further damage to his flesh).

Tomura's disintegration spreading through a crowd of individuals.

As the effect of Decay evolves, the spread grew beyond what the user had touched, creating a domino chain of disintegrated victims. Tomura had this ability ever since Decay first manifested on him, being strong enough to destroy an entire household. Still, due to his jumbled-up memories of the event, he seemingly either forgot about or mentally repressed this ability until halfway through the Revival Celebration, when flashes of his past started reminding him of what happened. When Tomura was a child, Decay's disintegration process was far weaker as it reduced affected _targets to chunks instead of dust.

The Quirk was initially perceived to be caused by a rare mutation that no one was aware of before it manifested. However, it was actually a reverse-engineered copy of Kai Chisaki's Overhaul Quirk. It originally contained the former Quirk's secondary power to reverse the effects, but Dr. Kyudai Garaki modified it from its original form before All For One secretly transferred it to Tomura, which left the Quirk purely destructive in nature.

Weaknesses

Because the Quirk required Tomura to physically touch an object to be activated, it was possible to counter Decay through Quirks that allow manipulating fluids or particles (such as Sandstorm), which Tomura cannot properly touch with his fingers. In addition, this Quirk was ineffective if the user wore a pair of gloves. Decay could also be countered if the affected area was destroyed before the disintegration finished spreading.

When Decay was used at full power, the disintegration effect could recoil and damage the user badly, as seen during the height of the Revival Celebration, when Tomura's Decay spread up his own arm, leaving it bloodied and scarred. Ever since Tomura received All For One and had his body completed, Decay had gotten so strong to the point that it started to slowly affect his body, as seen with the crack marks that formed on Tomura's face and skin.

Because the user's Quirk Factor lies within their hands, specifically their fingers, Tomura would lose the use of Decay if he lost them, similar to Overhaul. This weakness was subverted during the Final War, when Tomura underwent the Quirk Singularity and manifested large appendages coated in an array of fingers, which extended the reach of his Decay on a more devastating scale.

Usage

Young Tenko's Quirk manifesting, resulting in the death of his entire family.

The Quirk was secretly transferred to Tenko when he was five years old, one day while All For One was bringing him back home. After several days, it activated within him for the first time while he was playing with his dog, Mon. Tenko felt a shock through his left arm moments before getting physically punished by his father. While embracing Mon, Decay's effects materialized for the first time, resulting in Tenko accidentally killing his dog and then, later, his sister. Eventually, Tenko, resentful about his family and in a manic state, destroyed the rest of them and their household with his newfound Quirk.

All For One took advantage of this event to recruit Tenko (now Tomura) as his pupil and eventual successor when the latter was left alone and confused after the death of his family. With the help of his doctor and assistant, All For One was able to salvage the hands of the family members Tomura killed, using them as a sort of tool to help Tomura deal with his loss while simultaneously increasing his feelings of rage and hatred, which All For One believed was necessary for his plan to raise Tomura and his Quirk's strength.

As Tomura's memories of killing his own family were repressed by his subconscious, he became unaware of some aspects of his Quirk, unconsciously holding himself back from causing more destruction than he was capable of. As his past started sorting through his mind due to damage caused to his family's hands, Tomura started relearning and showcasing how truly powerful Decay is while battling against the Meta Liberation Army.

Tomura holding Izuku hostage. (Notice how one of his fingers is raised away from Izuku's neck.)

Decay is Tomura's primary method of combat. By nature, this Quirk forces Tomura always to engage his opponent in close quarters, though he often requires only to make contact with his enemy to kill or heavily injure them. Tomura has improved his Quirk since its first appearance at the Unforeseen Simulation Joint, as Decay's disintegrating speed has become noticeably faster in subsequent usages.

Tomura is often careful with his hands when touching objects he doesn't want to destroy, letting at least one of his fingers free from use while holding things. He employs a similar method when holding people hostage, threatening to disintegrate them if they don't comply or cooperate with him. If Tomura gets angered or frustrated, he will likely drop his carefulness.

Tomura re-awakening the original strength of his Quirk and going even beyond that.

Through vigorous training via several weeks of combat against Gigantomachia, Tomura has dramatically improved the strength of his Quirk. Decay works almost instantaneously now rather than taking several seconds before a _target crumbles to dust and continues to evolve under high-stress environments. Using his hands, everything Tomura touches is affected by Decay's spread; the function of which working in a solipsistic fashion where anything or anyone connected to what he's touching suffers its effects.

Even with his left hand partially destroyed, Tomura was able to decay part of Re-Destro's right index finger using only his left hands two remaining digits, albeit the process was much slower and weaker compared to when he uses all five fingers. By the end of his fight with Re-Destro, Tomura grew yet again, and his Decay is now strong enough to reduce nearly half a city to an ash cloud.

Tomura's Quirk growing powerful enough to devastate immensely large areas.

After All For One's Quirk was surgically grafted into Tomura's body, Decay became even stronger than before: its speed and range of effect increased so drastically that Tomura could spread the disintegration just by placing his hand on the floor. Such destruction allowed Tomura to destroy Jaku General Hospital while decaying everything inside before spreading to the nearby city. It has grown to the point anything touched and disintegrated spreads the effect even after parts of the crumbling matter break away and touch someone.

Tomura also has control over what gets explicitly affected by Decay, as he was seen wearing X-Less's cape despite the Hero being disintegrated. This enhanced control also allowed him to avoid deteriorating many of the Nomu in Dr. Garaki's laboratory, though he admits he couldn't save all of them.

During the Final War, Decay demonstrated its significant increase in power once again as Tomura was able to destroy a large chunk of the Shizuoka Prefecture by decaying beneath the surface, allowing the area to be washed away by the tides. After All For One seemingly destroys Tomura's spirit and gains back control of his body, he notes that Decay got destroyed alongside his rage and hatred due to Izuku attacking his soul.

Trivia

• Decay was a modified copy of Kai Chisaki's Quirk, Overhaul, which removed the restoration aspect, leaving only destruction. However, there are some key differences:
  • Decay's effects can spread to anything connected to a _target. Overhaul's effects are limited to the _target only.
  • Against a human opponent, Decay's effects will keep quickly spreading throughout their body with no way of stopping it save for mutilation of the affected area. Overhaul's effects happen instantly and can be contained within a specific body part.

External Links

• Decomposition - Wikipedia article about the concept behind Tomura's Quirk.