Why Nezuko is the key to Muzan's immortality in Demon Slayer season 4

Time of India

13-05-2025

Demon Slayer has certainly popularized anime, especially amongst a younger audience. For good reason, as
Kimetsu no Yaiba
has emerged as a true cultural phenomenon from Japan to the US, UK, and everywhere in between.
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It centers around Tanjiro Kamado, a compassionate adolescent who becomes a member of the
Demon Slayer Corps
after demons murder his family and transform his younger sister, Nezuko, into a demon. Unlike other demons, Nezuko is special—she doesn't injure humans and battles to protect them with her brother.
Yet by the end of Season 3, all of that gets turned on its head. For Nezuko, she's able to survive in the sunlight.
This is something that no other demon has been able to do. This revelation shakes the foundation of the entire world of Demon Slayer and lays the groundwork for a more sinister task for the series' ultimate antagonist,
Muzan Kibutsuji
. Now, his singular objective is to track down Nezuko, and take her power for himself before it's too late.
Nezuko's sunlight immunity stuns the Demon world
Sunlight has been the single, lethal weakness for demons in Demon Slayer for more than 1,000 years.
Regardless of how powerful they are, exposure to sunlight quickly turns them to ash—with instant incineration if exposed for too long. Even Muzan, the first and mightiest of demons, is afraid of the sun above all else.
By the end of the Swordsmith Village Arc in Season 3, Nezuko has begun to withstand the sunlight exposure and live. Having just defeated Upper Rank Four demon Hantengu, Tanjiro looks on in wonder as Nezuko steps into the sunlight unharmed.
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Surprisingly, she loses her blindness and her power of speech returns as well, and the first thing she does is smile at her brother.
This moment is certainly heartwarming, but its impact goes far beyond that. It completely alters the future of the entire series.
How is Nezuko able to walk in the sun?
Here are some scientific reasons as to why Nezuko, even as a demon, could be immune to sunlight.
While we may miss Muzan's blood During the attack on the Kamado family, Muzan injected Nezuko with a high concentration of his own blood. More blood than most demons get. This definitely could have accelerated her metamorphosis and evolution.
Nezuko heals from wounds with supernatural speed but has been gradually evolving into a more human form. Her body appears to be changing in a way no demon has before.
Unique hereditary abilities found within the Kamado family We know like the fact that the original Sun Breathing technique—the strongest form of swordsmanship in the Demon Slayer universe—was passed down through the original Kamado line. That helps to explain why Nezuko is so unusual.
No human flesh eating: Unlike other demons, Nezuko doesn't eat humans. She sleeps, replenishing her strength, which seems to have aided her in avoiding the typical demonic characteristics.
Combined, these factors create a unique demon in Nezuko—one who, unknowingly, might possess the cure Muzan has sought for ages.
Muzan's dark past: Why he fears death so much
Just remember, Muzan Kibutsuji wasn't always a monster. Long before he turned into the first demon, the now evil Muzan was a weak young man plagued by a terminal disease. A physician with unclear motives administered to him a treatment derived from a class of blossoms known as the
Blue Spider Lily
, which healed him. In the process, he became a demon himself.
This transformation endowed Muzan with supernatural strength and speed, but it did not grant him immortality.
Though he suffers from the petty dictatorship of his father, and though he still burns in the sun and he is always afraid of death. Since then, he has spent hundreds of years trying to locate the Blue Spider Lily once more, or develop a demon capable of withstanding sunlight.
All his efforts were in vain until now.
Why Muzan wants to absorb Nezuko in Demon Slayer season 4
As this new Season 4 rolls out, Muzan finds out that Nezuko has succeeded where he failed—she's learned to survive in the sun.
After diving into the memories of the fallen demon Hantengu, he eventually glimpses her transformation and becomes addicted.
At the end of the series, Muzan has no further need for the Blue Spider Lily. His plan is to absorb Nezuko so he can steal her immunity to sunlight and finally become truly immortal. If he has his way, he will be unstoppable.
This scary target alters the game completely. In this moment, Muzan now perceives Nezuko not only as a threat but as his only hope for survival.
The stakes going into season 4—Saving Nezuko's life at any cost
Along with Tanjiro, Nezuko has become the most popular character and even biggest star in Demon Slayer. If Muzan got her, he'd become the perfect being—immune to sunlight, invincible, unstoppable.
Now, the Demon Slayer Corps' greatest challenge lies ahead of them as they protect Nezuko while focusing on their final showdown with Muzan. With Season 4 starting out with the
Hashira Training Arc
, these elite swordsmen are all coming together to become even more powerful before the war approaches.
Tanjiro, Nezuko, and Hashira will have to stop him from letting Muzan bring the end of humanity now.
The future of Demon Slayer is up in the air
What this power does is it turns Nezuko into the most central, crucial character of the whole series. Muzan will stop at nothing to take her—and the survival of humanity may hinge on whether the Demon Slayers can defeat him.
Now that Demon Slayer is on the way to its ultimate climax, the stakes have never been higher.
Where to Watch Demon Slayer
Crunchyroll
Funimation
Netflix
Hulu
Season 4 is expected to cover the Hashira Training Arc and prepare fans for the final showdown in the Infinity Castle Arc.