In Demon Slayer: Kimetsu no Yaiba, no figure looms larger or more revered than Yoriichi Tsugikuni. He is a mythic warrior, a man who stood as the origin of the breathing techniques, and who nearly ended the demonic threat single-handedly. But beyond his ethereal skill and tragic life, a central symbol of Yoriichi’s legacy is his sword, a unique, pitch-black blade that burned with a crimson glow in battle. This weapon, intimately tied to his identity and power, represents not only his skill as a warrior but also the secret history of the Demon Slayer Corps.

This article explores the Yoriichi sword and its wielder:

Who Was Yoriichi Tsugikuni?

Yoriichi Tsugikuni was a samurai born during the Sengoku era, over 400 years before the events of Demon Slayer. He was born as the younger twin brother of Michikatsu Tsugikuni (later known as Kokushibo, the Upper Moon One), and from the moment of his birth, he was different. He bore the Demon Slayer Mark on his forehead, an ominous sign at the time, but later understood as a symbol of great power.

Unlike his brother, Yoriichi was soft-spoken, humble, and seemingly frail. But he held incredible latent power and an innate ability to sense the “Transparent World”,a mental state that allows the user to perceive the inner workings of a body, such as muscle movement and blood flow.

He also possessed unparalleled swordsmanship, and most notably, he was the creator of Sun Breathing, the original and most powerful of all Breathing Styles.

Yoriichi’s Sword: The Black Nichirin Blade

One of the most mysterious and significant aspects of Yoriichi’s character is his Nichirin sword. In the world of Demon Slayer, Nichirin blades are special weapons forged from scarlet crimson ore found in high altitudes, which absorb sunlight—a demon’s primary weakness.

Each sword changes color depending on the user's nature and breathing style.

A Sword That Held the Line of History

Yoriichi lived to an old age, wandering the land alone after the failure to destroy Muzan and the heartbreak of his brother’s betrayal. When he died, he was still undefeated in combat. His sword was placed at his shrine, along with a detailed memory of the Sun Breathing forms, which would be passed down through the generations.

This sword would eventually be discovered in the modern timeline by Tanjiro Kamado, the protagonist of the series. Housed within a mechanical doll known as Yoriichi Type Zero, the blade reemerges after centuries, carrying with it the ghost of the past and the hope of future victories.

Symbolism of Yoriichi’s Sword

Yoriichi’s sword is a metaphysical totem. It represents the origin of the Demon Slayer legacy, the sorrow of failed salvation, and the immense burden of impossible standards. Black and red, sun and death, hope and mourning—it embodies all the contradictions of Yoriichi himself.

Its transformation into a crimson red blade is a visual metaphor for Yoriichi’s unique position: a bringer of light through a path of blood. The blade is as much a character in the story as he is—a constant reminder that true power is often born from deep suffering and sacrifice.

A Blade for the End of All Demons

Yoriichi’s sword, like the man himself, is a once-in-a-millennium phenomenon. Though silent now, lying dormant in Tanjiro’s hands, its spirit continues to blaze through the fight against Muzan and the Twelve Kizuki.

The sword reminds us that Demon Slayer is not only about combat, it is about legacy, grief, and the fragile line between heroism and tragedy. Yoriichi’s blade is the first and final word in that legacy. It is the tool that almost ended Muzan’s reign and the key to the future redemption of humanity.

As Tanjiro takes up the sword and steps into the Transparent World, he is fighting with the will of the Sun itself, passed down by the only man who ever made Muzan afraid.

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