Decay allows Tomura to destroy anything his hands touch, making it crumble to dust.
Whether the target is organic or not, Decay will work without fail. As such, this Quirk is extremely lethal against living beings, having their flesh rot away if hit by it. The speed of the disintegration has varied from slow to almost immediate, eventually spreading through their whole body if a victim doesn't amputate the decaying body part.
Decay will only occur when all five fingers touch the target, indicating that its activation isn't voluntary, or at least that Tomura's control is clumsy. Because the Quirk requires to touch a solid object in order to be activated, it is possible to counter Decay through Quirks that allows manipulation of fluids or particles, which Tomura cannot properly touch with all his fingers.
Decay stays permanently on a target, once they have been touched everything part of it will be infected as well, even if Tomura is not touching the target anymore. Pro Hero Aizawa avoided this by erasing Tomura's Quirk to prevent the decaying process from spreading even further,
Decay is Tomura's main method of combat. By nature, this Quirk forces Tomura to always engage his opponent in close quarters, though he often requires only to make contact with his enemy in order to kill or heavily injure them.
Tomura seems to have improved his Quirk ever 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 crumble down, 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 is likely to drop his carefulness.
- ↑ My Hero Academia: Battle For All Official Website
- ↑ My Hero Academia Manga and Anime: Chapter 69 and Episode 38.
- Decomposition - Wikipedia article about the concept behind Tomura's Quirk.