Quirk-Destroying Drug

The Quirk-Destroying Drug attacks the genetic machinery a Quirk runs on. It came out of the Shie Hassaikai, the Yakuza outfit run by Kai Chisaki, called Overhaul, who conceived the thing and sourced it from the biology of a child named Eri.

Delivery is narrow. The drug travels in red cartridges tipped with hypodermic needles, and a hit ruins the Quirk almost at once. Kai built the counter as well, a serum that undoes the damage and hands back what was taken. There is one cruder escape, which is to stop the spread through the blood before it arrives, and Shota Aizawa took that route by dismembering his own leg.

Kai's plan for the pair of products was a market he controlled from both directions. Villains would buy bullets and spend them on Heroes. The Yakuza would then let the serum find its way to those same Heroes, at a price. With Eri sitting in the middle of the arrangement, the Shie Hassaikai would take money off everyone, restore the organization's old standing, and put a real fear into a population that has built its entire life around having a Quirk. Both products were priced accordingly.

A permanent cure eventually surfaced, and it came from the other side. Shota Aizawa reasoned that Rewind, the Quirk the drug was grown from, ought to be able to return a ruined Quirk Factor to the condition it held before. Eri spent months learning to control the ability, then gave Mirio Togata his Quirk back, which leaves her the only known remedy.

Kyudai Garaki turned the same research sideways. Reading past the weapon to the Quirk underneath it, he produced a single-use Rewind Drug for All For One, one that reverses damage in the body while ignoring the Quirk Factor entirely.

Kai Chisaki started it by asking his boss for the man's granddaughter, whose Rewind Quirk had come in strange, as raw material. The refusal was on ethical grounds. Kai put the old man down and took the organization for himself. Harvesting her through his own Overhaul Quirk, which let him take her apart and restore her without limit, the Shie Hassaikai reached a prototype that switched a Quirk off for a few hours, and those went out in bullets for testing only. Funding was the constraint, and the League of Villains supplied it, having seen the prototype work firsthand when the two groups clashed. The finished version was permanent, and the serum arrived beside it.

Shin Nemoto fired the shot that proved the point. Cornered during the raid on the Shie Hassaikai stronghold by Mirio Togata, who caught him before he could slip away, Kai had Nemoto put a loaded bullet into the young hero, and Permeation was gone for good. It bought Kai nothing. He lost the fight anyway and the Police Force impounded the drug, at which point the League ambushed the convoy carrying him and the case, and walked away with both.

Tomura Shigaraki wanted more of them than he had. Jin Bubaigawara tried running them through Double, but with no data on the drug and no accurate image of it, the copies fell apart within moments, and he apologized for failing to mass-produce what Tomura wanted. So Tomura went after Kyudai Garaki, the doctor behind the Nomu and All For One's keeper, who did manage to replicate the bullets. Most of that stock melted when X-Less reached them during the Jaku General Hospital raid, and Tomura, hearing of it, remarked that Overhaul would be disappointed. The last two went with him into the fight against the Heroes. He threw one at Eraser Head and held the other for Enji Todoroki, though Katsuki Bakugo detonated that one in the air before it landed. Aizawa's found his leg, and he cut it off himself rather than lose Erasure. That appears to have exhausted the supply.