Muzan Kibutsuji, the Demon King in Demon Slayer: Story, Powers, and Obsession with Immortality

From a weak human constantly seeking ways to survive, he transformed into the Demon King, a cruel, cunning figure and a source of suffering for humanity.

Origins: Born in Suffering

Muzan’s story begins in the Heian era, over a thousand years ago. Even in the womb, he faced worrying conditions: a heart that often stopped and a fragile body. At birth, doctors nearly declared him dead until he suddenly cried before cremation. Throughout his childhood and adolescence, a mysterious illness continuously weakened him. Doctors were pessimistic about him reaching the age of 20. In despair, he accepted experimental treatment using Blue Spider Lily, a rare flower that would later change his fate and the world.

Transformation into a Demon

The experimental medicine gave Muzan extraordinary powers: a body that healed, strength, and longevity but with terrifying side effects. He became thirsty for human blood and could no longer tolerate sunlight; exposure to sunlight would burn his body to ashes. He killed the doctor treating him before learning the full formula of the Blue Spider Lily, thus losing the chance to perfect an antidote to his weaknesses. From there, Muzan was born as the first demon, and from his blood, hundreds, even thousands of other demons were created.

Unusual Powers and Anatomy

As the progenitor of all demons, Muzan’s power far surpasses ordinary beings. Some of his main abilities:

• Extreme regeneration: He can regenerate body parts like his head within seconds and recover from seemingly fatal damage.

• Biokinesis / body manipulation: Muzan can change his physical form, disguise as a man, woman, or child complete with voice and behavior, making him almost undetectable.

• Unique anatomy: Muzan’s body has additional organs, reportedly having seven hearts and five brains, so attacking him is not simple as these organs can shift positions.

• Telepathy and control: He can communicate with demons he created, see through their eyes, and even kill them remotely by his will.

• Blood that affects DNA: Muzan’s blood is deadly to some; others transform into demons if they survive but then must prey on humans to survive.

Obsession with Blue Spider Lily and Immortality

Muzan’s main goal after becoming a demon was to eliminate his greatest weakness: sunlight. The Blue Spider Lily was considered the key. However, the flower blooms rarely, only 2–3 days per year, and only during the day, making the search practically impossible. To overcome this, Muzan created many demons hoping one would find the flower or develop resistance to sunlight. He also infiltrated the human world, stealing identities of wealthy people to fund research and exploration. When Nezuko Kamado showed the ability to withstand sunlight, Muzan immediately targeted her, considering her body the key to removing that weakness.

Terrifying Forms and Survival Strategies

Muzan can manipulate his body into terrifying forms: from tentacles ending in mouths and eyes to a massive flesh mass full of mouths emitting electric waves and energy attacks. At the climax of battle, he even transforms into a giant demon baby, a seemingly embarrassing form but actually a last strategy to protect his core body.

Final Battle and Muzan’s Fate

The final confrontation between Muzan and the Demon Slayer Corps marked the end of the dark era. Tamayo and Shinobu, through extensive research, succeeded in creating a special poison that accelerated Muzan’s aging: the poison made him age decades every minute, reportedly about 50 years per minute, and during the conflict, it eventually aged him about ~9,000 years total, weakening his regenerative abilities.

With that chance, Tanjiro and the Hashira launched an attack including breathing techniques inherited from Yoriichi Tsugikuni and held Muzan until dawn. When the sun rose, Muzan’s body burned to ashes. Before vanishing, Muzan tried to transfer his blood and memories to Tanjiro in a desperate attempt to preserve his existence. Muzan’s death also marked the disappearance of almost all demons he created, due to their connection through his blood.

Muzan’s journey from a fragile human to the ruler of darkness is a story about trauma, fear of death, and obsession with immortality that turns into destruction. He is not just a powerful enemy to be defeated; he is an extreme reflection of how fear and despair can breed brutality.

For fans of the series, the anime version of Muzan will most likely reach his final fate in the Infinity Castle Part 3 film adaptation, a wait mentioned to happen in 2029. Meanwhile, his story remains one of the most complex and iconic antagonists in the world of Demon Slayer.