How do you become a demon in Demon Slayer?

The demons of Demon Slayer are not creatures from elsewhere. All of them were humans, with a name, a family, a trade, and all became demons in the same way. Understanding this transformation sheds light on almost the whole story: why Nezuko attacks her brother on the first morning, why demons forget who they were, why Muzan sees through their eyes, and why the ending of the series hinges on a cure.

Here is what happens, step by step, when a human becomes a demon, then the rules that weigh on them and the rare cases that escape them. Our page on the Demon Slayer demons presents Muzan and his Moons, and our article on Nezuko’s transformation into a demon tells the night it all begins for the Kamado family.

A single creator, Muzan Kibutsuji

All the demons of Demon Slayer descend from one. A thousand years ago, in the Heian era, Muzan Kibutsuji was a young man doomed by illness. A doctor gave him an experimental remedy, one of whose ingredients was a rare flower, the blue spider lily. Impatient at not recovering fast enough, Muzan killed the doctor before the end of the treatment. Yet the remedy had worked: it had made him immortal, stronger than a man, and unable to bear sunlight.

Muzan spent the following centuries searching for the missing flower, to finish the treatment and overcome the sun. He also discovered that he could pass his condition on to others by giving them his blood. Every demon in the series therefore carries a part of Muzan. Our article on the blue spider lily tells this thousand-year quest, and the one on Muzan Kibutsuji, the first of the demons traces his life.

The blood and the dose

In Demon Slayer, the transformation comes down to one gesture. Muzan drives a finger or a claw into a human’s skin and injects his blood. Sometimes he does it to a passer-by in an alley, sometimes to a fighter he has chosen. His Upper Moons can pass on this blood in turn: Doma turned Gyutaro and his sister Ume, the future Daki, and Kokushibo made Kaigaku a demon. But it is always Muzan’s blood that does the work.

The Asakusa scene shows how quick the gesture is. To create a diversion when Tanjiro recognises him in the crowd, Muzan scratches a passer-by’s neck. The man turns into a demon in a few seconds and throws himself on his own wife, and Tanjiro has to pin him to the ground to stop him devouring her. Muzan, meanwhile, calmly walks away arm in arm with his borrowed family.

The dose decides everything. Too much blood, and the body cannot hold: the cells break down and the recipient dies in atrocious pain. Just enough, and the human wakes up a demon. The more blood they received, the stronger they are from the start, and the more they can receive later to rise in rank.

This is what happens to Enmu, Lower Moon One. On the evening Muzan executes the other Lower Moons, Enmu thanks him for killing him, and Muzan, amused, instead gives him a new dose of his blood, with a mission: to kill the boy with the hanafuda earrings. Enmu comes out of that night stronger than he went in. Our article on the Lower Moons executed by Muzan tells that meeting.

What changes in the body

The new demon stops ageing. Their wounds close in a few moments, a severed arm grows back, a split head knits back together. They become much stronger and faster than a human. Their eyes often change, with slit pupils, and some bodies become deformed: horns, extra arms, mouths that open in the palms.

In exchange, they fear only three things. The sun reduces them to ashes in a few seconds, which forces them to hide by day. A Nichirin blade, forged from an ore that has absorbed sunlight, can cut off their head, and it is the only way to kill them with a weapon. Wisteria, lastly, weakens them: demons flee its flowers, and Shinobu draws from it the poison she injects with her sword.

In Demon Slayer, demons who have devoured many humans also develop a power of their own, the Blood Demon Art. It takes the form of a weapon, a spell or an illusion, and often reflects what the demon was or longed for in life: drums for Kyogai, the failed writer, threads for Rui, who wanted a solid family. Our article on the demons’ Blood Demon Arts presents them one by one.

The hunger for human flesh

The first effect of the transformation is hunger, the driving force behind almost every fight in Demon Slayer. A demon must eat human flesh to live and to grow stronger. On waking, this need is so violent that they throw themselves at the first humans within reach, often their loved ones. That is why so many demons in the series began by killing their own family, and why Tanjiro finds Nezuko ready to bite him on the first morning.

The more a demon eats, the stronger it becomes. Some count their victims, like the Hand Demon of Mount Fujikasane, others prefer young women, whom they find more nourishing, like Doma. The blood of certain humans, the marechi, is worth dozens of meals on its own. Sanemi Shinazugawa is one of them: his blood intoxicates demons, and he uses it as a weapon by cutting his own arm. Our article on whether Nezuko eats humans explains how she manages without.

Hunger also weighs on demons who do not want to kill. Tamayo has altered her body so that a little blood is enough, which she buys from people in need. Nezuko, for her part, recovers her energy by sleeping, sometimes for days on end. These two cases show that hunger is a law of the body, not a moral fate.

Memory that fades

In Demon Slayer, Muzan’s blood also eats away at memories. Demons gradually forget their human life, their name, those they loved. Some keep an emotion without knowing where it comes from: Akaza refuses to eat women without knowing he loved Koyuki, Rui wants a family without remembering he killed his own.

Very often, memory returns at the moment of death. The Hand Demon of Mount Fujikasane remembers his big brother, Rui the parents who wanted to die with him, Akaza Koyuki and his dojo master, Daki and Gyutaro their wretched childhood. Tanjiro is often the witness of these last moments. He smells their sadness, and sometimes lays a hand on them as they disappear, as on the hand of the Final Selection demon or on Rui’s back.

Rui pushes the logic to its limit. He gives part of his blood and powers to other demons so that they play his family, a father, a mother, sisters, and forces them to take on his appearance. This blood bond only creates a family of terror, punished at the slightest misstep. Our article on Rui and his spider family tells the story of this demon who wanted bonds.

The curse of the name

All the demons of Demon Slayer remain bound to Muzan by his blood. He sees through their eyes, hears what they hear, reads their thoughts when they are close and can kill them by sheer will. To protect himself, he has placed a curse on them: a demon who speaks his name in front of someone dies at once, destroyed from within by their master’s cells.

Susamaru learns this the hard way. In Asakusa, sent by Muzan with Yahaba to kill Tanjiro, she falls for one of Tamayo’s spells and shouts her master’s name. Arms burst from her own body and tear her to pieces before Tanjiro’s eyes. The six-armed demon with her temari balls dies for a single word.

Only a few demons escape this bond. Tamayo freed herself from it through her own blood science, at the cost of centuries of work. Nezuko seems to have escaped it on her own, perhaps thanks to her will and her long convalescence. Our article on Susamaru and Yahaba, the Asakusa demons tells that fight, and the one on Tamayo, the demon doctor presents the woman who broke the curse.

The blood hierarchy

The strongest demons in Demon Slayer make up the Twelve Kizuki, the Juni Kizuki. Six Upper Moons and six Lower Moons, each with its rank engraved in its eye. This rank depends on the amount of blood Muzan has given them and on their strength in combat. A Lower Moon can challenge an Upper Moon to take its place, and the winner takes its rank.

Muzan remains the sole master of this hierarchy. He rewards with his blood, punishes with death, and disbands entire Lower Moons when they disappoint him. The Upper Moons, for their part, had not changed for more than a century before the death of Daki and Gyutaro. Our article on the Twelve Kizuki presents each of them.

The exceptions

A few Demon Slayer characters escape the rules. Nezuko never eats a human, protects humans instead of attacking them, and ends up withstanding the sun in the Swordsmith Village, the first in all of history. Muzan hunts her at once, because she has what he has been seeking for a thousand years. Tamayo, turned by Muzan several centuries ago, freed herself from him and created a single demon, Yushiro, a dying young man she saved by turning him.

Two demon slayers complete the list. Genya Shinazugawa eats demon flesh to borrow their powers, without ever becoming a demon himself. Tanjiro, at the very end, is turned into a demon by the dying Muzan, then brought back by the cure and by Nezuko’s voice. Our article on demon slayers turned demons tells these crossings from one side to the other, and our page on Nezuko Kamado, Tanjiro’s sister traces her path.

Can you become human again?

For almost the whole of Demon Slayer, the answer seems to be no. Demons killed by demon slayers die in ashes, with no way back. Yet from the very first day Tanjiro clings to the idea of making Nezuko human again, and Tamayo proves him right in Asakusa: she has been working on a cure for centuries, and asks him for blood samples from the demons closest to Muzan.

This cure comes about during the Hashira Training, prepared by Tamayo with Shinobu’s help. Nezuko receives it and becomes human again during the final battle. Another version, which weakens and ages Muzan, is injected into him by Tamayo herself. The cure is used one last time for Tanjiro, at dawn. The transformation is therefore reversible, but at the cost of a thousand years of waiting and Tamayo’s life. Our page on Tanjiro Kamado, the hero of Demon Slayer tells the quest that leads to this cure.

To play a demon in cosplay, measure yourself and rely on the sizes on the product page, and take care with the details that betray the transformation: the eyes, the marks, the claws. Our demon cosplay collection gathers Muzan, Akaza, Doma, Kokushibo and Nezuko, our demon figure collection the Moons as figures, and our Muzan Kibutsuji Demon Slayer collection everything to do with the first demon. Items are delivered in 5 to 12 days depending on where you live, and our Demon Slayer cosplay range gathers all the outfits.