In Demon Slayer: Kimetsu no Yaiba, swords are more than just weapons. They are extensions of their wielder’s spirit and breathing style. Few blades are as mysterious and significant as the one connected to Yoriichi Tsugikuni, the legendary first user of Sun Breathing.

In the third season, Tanjiro stumbles across a centuries-old sword hidden within the Yoriichi Type Zero combat doll, raising questions about whether it is the real Yoriichi sword, its true color, and why this weapon seems to change in appearance.

The Sword’s Discovery

During Tanjiro’s grueling training with the Yoriichi Type Zero doll, he finally manages to push past his exhaustion and slice through the doll, and uncovers a hidden sword sealed inside for over three hundred years.

Many fans immediately suspected that this was Yoriichi’s very own weapon, preserved from a time long past.

But Is It? Why the Sword’s Appearance Differs

Flashbacks in the anime show the Yoriichi sword has distinctive features: a gold-dipped hilt with a textured grip, a rectangular guard, and a black sheath. Yet the blade Tanjiro retrieves looks very different.

Its crossguard is circular, its handle is wrapped in yellowed cloth rather than gold, and its sheath is white rather than black. These details cast doubt on whether the sword is truly Yoriichi’s original.

The discrepancies may be explained by centuries of maintenance—or neglect. Over time, fittings could have been replaced, wrappings deteriorated, and decorative gold stripped away. The Kotetsu family, descendants of swordsmiths who maintained the doll, might have altered or repaired the blade across generations.

With no official explanation given, the anime leaves viewers to accept that despite these cosmetic differences, the sword is indeed tied to Yoriichi’s legacy.

The Restoration of the Blade

Once uncovered, the eccentric swordsmith Haganezuka works obsessively on reviving the sword to its prime state. When complete, the blade regains its brilliance and is refitted with a new guard, one gifted from the Rengoku family, carrying the flame design once belonging to Kyojuro Rengoku.

The Black Blade and Its Transformation

When Tanjiro finally wields the reforged sword, its true nature becomes clear. The blade turns black, the rarest and most enigmatic Nichirin color. Black swords are often considered unlucky, as their meaning was historically unknown.

Yet with Tanjiro, the black blade reflects his connection to Sun Breathing, the original technique from which all others descend.

What makes this sword even more remarkable is its ability to glow red with a flame-like pattern under certain conditions. This transformation mirrors the ability once displayed by Yoriichi himself.

The change occurs when the user pushes beyond ordinary limits, channeling an intense life force into the weapon. The red hue not only increases the sword’s cutting power but also allows it to nullify demons’ regenerative abilities, making it one of the most lethal tools in existence.

Why the Color Change Matters

The shifting colors of the sword symbolize Tanjiro’s growth. Early in the series, his blades often shattered, either because of his inexperience or because they could not withstand the strain of Sun Breathing.

With Yoriichi’s sword reforged and awakened, Tanjiro finally wields a sword that matches his potential. The black foundation represents his path as a Sun Breather, while the red glow signifies the awakening of his deeper power, linking him directly to Yoriichi’s legacy.

The real color of Yoriichi’s sword is not simply black or red; it is both. Black is its natural state, rare and mysterious, but when wielded at its peak, the blade shifts into a blazing red, echoing the flames of the sun itself.

This duality makes the weapon a perfect reflection of Yoriichi and Tanjiro: warriors who fight not for glory, but to bring light into a world plagued by darkness. The color change is not just cosmetic; it is a sign of the wielder’s bond with Sun Breathing, their resolve, and their will to destroy demons at the root.

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