How Muzan became a demon in Demon Slayer: The dark origin of anime's most terrifying villain

Time of India

09-05-2025

How Muzan became a demon in Demon Slayer: The dark origin of anime's most terrifying villain
Credit- Fandom
As the greatest scourge and antagonist of
Demon Slayer
,
Muzan Kibutsuji
, he certainly seems like one, but this deadly villain wasn't always one. His change from a quiet, fading human to the
first demon
is one of anime's darkest origin stories.
Taking place in Japan during the early 1900s, set in a world where most humans have been wiped out, Demon Slayer follows a young boy whose family gets slaughtered by these deadly demons.
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These demons tear apart humans, possess magical powers, and can only be killed in the light of day or with specially crafted weapons. Based on the manga by
Koyoharu Gotouge
, the series tells the story of
Tanjiro Kamado
, a kindhearted boy whose family is brutally slaughtered by demons, save for his sister
Nezuko
, who is transformed into one herself.
Yet all demons in this world stem from the same root: Muzan Kibutsuji, the first and most powerful demon. While Muzan has a pretty expansive role, he's known as the Demon King, and he's the primary antagonist of the narrative. What caused him to turn into a demon to begin with?
Muzan was once human—And afraid of death
Muzan wasn't always a demon. He lived over a millennia ago in Japan's Heian Period (794–1185). To say that infanticide was the least of Muzan's problems is an understatement, from the very start, Muzan's life was a challenge. Before he was even born, Blake's heart stopped in the womb. When he was finally born, he was pronounced stillborn until he began breathing on his own, defying all odds of supposed inevitable death.
As a young man he contracted an equally lethal disease that was sure to take his life before he reached the age of 20. A doctor, in a desperate attempt to save him, gave him a strange experimental medicine made from the very rare blue spider lily, his poisonous curse. Annoyed that it was worthless, Muzan, in a fit of anger, murdered the doctor before discovering that the treatment had been a success.
The origins of the first demon
The miraculous medicine came with horrific side effects, as it cured Muzan's illness. He was unable to walk in sunlight and had an insatiable appetite for human flesh. These changes made him the very first demon.
Muzan soon realized that eating humans not only replenished his strength but made him more powerful, and with these new abilities, he became invincible. One thing continued to be his biggest nemesis: the sun. There, he learned that exposure to sunlight would kill him instantly.
Despite all of his powers and abilities, Muzan was afraid of death above all. This fear turned into his obsession. Now, to become truly immortal, he needed to defeat his weakness to sunlight. He spent centuries attempting to recreate and improve upon the original doctor's formula, but the blue spider lily was gone, and the doctor's secrets perished with him.
Muzan's eternal quest for perfection
Muzan wasn't content to survive, he wanted a perfect body, one that never needed to develop, never withered or aged, with no hint of fragility. Here's what he states in the Demon Slayer manga:
Illustration by Daniel Horowitz 'The one thing I like is change… The one thing I dislike is permanence.
So he invented additional demons with the intention of having one of them develop past their vulnerability to sunlight. This explains why he created the
Twelve Kizuki
, his own army of elite demons, and why he fixated on Nezuko. When he found out that Nezuko even as a demon could roam freely under the sun, Muzan considered her to be the solution to his problems, finally allowing him to reach his goal of becoming an unstoppable, eternal being.
Muzan's origin is tragic and terrifying.
Muzan's origin contributes to him being more than a run-of-the-mill anime villain. He wasn't born a monster. He was a starving man hell-bent on survival. That same desperation drove him to ruin the lives of billions, birth an army of demons, and almost conquer the world.
It's one of the sad truths of superhero storytelling that his story teaches fans—that most of heroes' greatest foes are born out of pain, fear and decisions turned sour.
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