Black Nichirin Swords in Demon Slayer were not inherently bad, and their bad reputation is thanks to Muzan

The Demon Slayer series features a very broad narrative that spans multiple storylines from both the past and present. One of the most talked-about facts is the curse of the black Nichirin swords. It has been passed down through generations that Slayers with a black sword tend to have a very short lifespan and die earlier than those without.

However, the true origins of the black sword are different, and rather more empowering than a curse. Due to a lack of understanding, Demon Slayers have died young in the past, with Muzan playing a key role in their deaths.

Disclaimer: This article contains potential spoilers from the Demon Slayer anime and manga.

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The Black Nichirin Swords hold a significant role in the Demon Slayer universe

The Demon Slayer universe carries forward the concept that all black Nichirin sword users have a short life span from past instances. The blade is treated as a curse, bringing early death to the user. However, the true significance of the black sword is something else, which some fans may have forgotten.

The black Nichirin sword, in reality, signifies the user having the potential of learning and using the Sun Breathing technique, the most powerful Breathing Form of the series. However, the Slayers and others were oblivious to the information, even the Ubuyashiki household.

What might have happened is due to a lack of information; the Slayers chose a different path for themselves, trying to learn a different Breathing Form, straying completely from the intended use. Misguided or uninformed, these Slayers might have met an early end. Furthermore, Muzan also made a key contribution to turning the myth into a reality.

With his first encounter with Yoriichi Tsugikuni, the original user of the Sun Breathing or Hinokami Kagura technique, Muzan realized how devastating the style could be. The Hinokami Kagura mimics the elemental powers of the Sun, which demons fear and is their greatest threat. This is the only technique capable of defeating someone immune to beheading, like Muzan.

To make things easier and eliminate a major obstacle to his goals, Muzan and the Upper Moon One demon Kokushibo set out to kill all Sun Breathing demon slayers. Whether Muzan knew of the black sword's connection to the Sun Breathing technique is unclear, but it’s safe to assume he suspected it from his previous encounter with Yoriichi, who also wielded a black sword.

The mistaken belief that the black sword is linked to the Sun Breathing form has led to missed opportunities in the series. The most notable example from the current generation is Murata. Although his status remains unknown and the story does not explore his potential as a Sun Breathing user, his black sword suggests he might have it.

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Final thoughts

Knowing that the black Nichirin sword is one of the most powerful weapons against the demons, it is likely that the Demon Slayer series tried to nerf it by adding a curse so that it doesn't become an overpowered weapon. Nevertheless, the true importance of the sword is its potential for Sun Breathing, not that the users die young, which is something Muzan helped instigate.

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