Anti-Kibutsuji Drug

The Anti-Kibutsuji Drug is a four-layered compound produced through the combined medical knowledge of Tamayo, Yushiro, and Shinobu Kocho. Its single goal is the destruction of Muzan Kibutsuji. Work on it intensified after the assault on the Swordsmith Village, and it saw use during the final battle within the Infinity Castle.

Anticipating that Muzan would likely consume her body, Tamayo introduced the compound into her own flesh beforehand. When he absorbed her arm, he unknowingly took the drug with it, setting its stages in motion.

The drug works in four stages, each triggered once the previous one has taken hold of its target.

Human Regression

Developed before it was even needed, this first stage aimed to turn Muzan back into a human. Its creation drew on the blood of powerful demons carrying high concentrations of Muzan's blood, along with Nezuko Kamado's blood. Once Tamayo joined forces with Shinobu, the effect grew far stronger. Muzan managed to neutralize it, but doing so accidentally unlocked the remaining stages.

Accelerated Aging

Proposed by Shinobu, this stage forced rapid aging on Muzan. Though aging means little to a regenerating demon, it compelled him to pour power into keeping his body battle-ready. Across roughly three hours it pushed his physical age forward by an enormous span, sapping the stamina that had once seemed limitless and letting the wounded Hashira keep pace with him.

Division Prevention

Crafted by Tamayo after she observed how Muzan once survived Yoriichi Tsugikuni by splitting into countless fragments, this dormant stage blocked him from breaking apart to escape. He only realized it when he tried to divide himself and failed.

Cellular Destruction

The final stage broke Muzan down at the cellular level. With his immortality already weakened, his regeneration slowed dramatically, and even a standard Nichirin Sword could inflict lasting harm. Together the four stages held the fight off until sunrise, letting the Demon Slayers corner and finish him.

Tamayo deployed the drug, carrying part of it within her own body so Muzan would ingest it when he absorbed her. The creation involved Tamayo, Yushiro, and Shinobu Kocho. Both the manga (Chapter 138) and the anime (Episode 63) depict its introduction during the war against the Demon King.