Muzan Kibutsuji wasn't killed by a single sword strike, despite the countless blades swung against him during the final hours of the Infinity Castle arc. The ultimate destruction of the Demon King was a collaborative execution engineered by Lady Tamayo's specialized four-stage drug, sustained by the sheer sacrifice of the Demon Slayer Corps, and finalized by the natural light of the rising sun. If you want to understand who actually brought down the most feared entity in the Taisho era, you have to look past the protagonist's final stance and examine a web of medical sabotage and suicidal tactical defense.
The Cumulative Poison of Lady Tamayo
No discussion of Muzan's defeat holds weight without recognizing Lady Tamayo's absolute central role. For centuries, Tamayo dedicated her existence as a demon to formulating a cure and a weapon capable of dismantling Muzan from the inside out. Working alongside Shinobu Kocho and Yushiro, she engineered a complex, multi-layered drug administered directly into Muzan's body during the early stages of the final confrontation.
This drug didn't just act as a standard poison. It functioned as a biological demolition kit with four distinct vectors:
- Aging acceleration: The drug forced Muzan's cells to age at an unnatural rate, aging him by roughly nine thousand years per minute of combat. This robbed him of his peak physical speed and regenerative efficiency.
- Cellular division blockage: It prevented his flesh from splitting, spawning new combat forms, or easily repairing severe structural damage.
- Shockwave paralysis: Periodic bursts within his bloodstream paralyzed his internal organs and slowed his reaction times during critical moments against the Hashira.
- Anti-regeneration suppression: It blocked his demonic cellular adaptation, leaving him vulnerable to physical destruction that he would have shrugged off effortlessly decades prior.
Without Tamayo's sacrifice—giving her life so the drug could be injected—the Hashira would have been slaughtered within minutes. The poison turned an immortal god into a mortal timer ticking down to zero.
The Brute-Force Human Shield: The Hashira and Tanjiro
Even with Tamayo's drug aging him rapidly, a weakened Muzan remained an apocalyptic threat. He possessed devastating shockwave attacks capable of slicing through multiple elite swordsmen simultaneously. This is where the remaining members of the Demon Slayer Corps became the literal human anchor holding him in place.
Gyomei Himejima, Sanemi Shinazugawa, Giyu Tomioka, Obanai Iguro, and Mitsuri Kanroji pushed past their physical limits, suffering catastrophic injuries. They weren't trying to cut off his head—by this point, everyone knew beheading Muzan was useless. Instead, they treated themselves as living hooks. Their only objective was to intercept his escape routes, block his burrowing attempts, and keep him locked in the open air as the eastern horizon began to brighten.
Tanjiro Kamado played the central anchoring role during these final, frantic minutes. Even after losing an eye and absorbing massive amounts of damage, he pinned Muzan's movements with his Nichirin blade, driving it deep into the monster's chest despite having his own flesh torn apart.
The Executioner: Sunlight
When people ask who killed Muzan, the literal answer is the sun. No human breathing style or special sword technique could permanently stop his cellular regeneration. It was daylight that finished the job.
As dawn broke over the battlefield, Muzan realized he couldn't overpower the remaining slayers and escape underground. In a panic, he bloated his flesh into a massive, infant-like meat shell to shield his true core from the photons. The surviving slayers, along with support staff from the Kakushi unit, threw their bodies onto the monstrous mass to prevent it from crawling into the shadows.
The moment direct sunlight hit Muzan's flesh, his cells began to char, disintegrate, and vaporize into nothingness. The centuries-long terror dissolved into ash, proving that nature itself executed the sentence the Corps engineered.
Muzan's Final Act: The Demon King Parasite
Muzan's death wasn't a clean exit. Realizing his physical body was turning to dust, he committed his final, desperate act of self-preservation. He forced all remaining consciousness and a torrent of his concentrated blood into Tanjiro Kamado, transforming him into a creature that possessed ultimate demonic immunity—including the ability to conquer the sun.
This created a terrifying narrative twist: for a brief window, Tanjiro was Muzan's legacy. The Demon King's spirit whispered inside Tanjiro's mind, begging him to stay a monster and live forever.
[Muzan's Poison] + [Hashira Endurance] ---> [Sunrise Execution] ---> [Tanjiro's Brief Infection] ---> [Final Dissolution]
The true end of Muzan only arrived when Kanao Tsuyuri successfully injected the remaining human-restoring medication into Tanjiro, and the collective emotional bonds of his friends pulled his consciousness back from the brink. As Tanjiro returned to humanity, the last shred of Muzan's will withered away into absolute nothingness. You can explore more background on the Official Demon Slayer Portal to see how character arcs tie into this final sequence.
Frequently Asked Questions
Could Yoriichi Tsugikuni have killed Muzan permanently?
Yes. Centuries before the main storyline, Yoriichi pushed Muzan to the absolute brink using his Sun Breathing techniques and transparent world perception. Muzan only survived that encounter by tearing his body into nearly eighteen hundred pieces, escaping with a fraction of his power, and hiding for decades out of pure terror.
Why didn't normal Nichirin swords work on Muzan?
Muzan's biology allowed him to alter his internal organs, heart placement, and brain structure at will. Standard beheading techniques failed because his body did not rely on a single vital point. Only the combination of Tamayo's cellular poison and direct exposure to ultraviolet sunlight could bypass this defense.
Did any other demons survive Muzan's death?
Yes. Because Muzan's death triggered the collapse of all demons created by his direct bloodline, nearly every demon vanished. However, Yushiro survived because Tamayo turned him into a demon using her own independent methods, making him entirely unlinked to Muzan's hive mind.
What happened to Tanjiro's arm after the battle?
Due to the intense trauma, physical stress, and necrotic damage sustained while fighting Muzan and undergoing temporary demonic transformation, Tanjiro lost full functional mobility in his right arm and permanent sight in his right eye, marking a permanent physical toll for his victory.
