Nichirin Sword

Nichirin swords, along with other Nichirin weapons, are the primary tools the Demon Slayer Corps uses against demons. They are made from Scarlet Crimson Iron Sand and Scarlet Ore, materials gathered on high peaks such as the perpetually sunlit Mount Yoko. The name combines characters for sun and ring, often read as solar, paired with the character for blade, giving roughly the meaning of solar blade.

The ore is thought to draw on Hihiirokane, a legendary metal of Japanese myth said to shine like flame or the sun. After a Slayer rises to Hashira, their weapon may be engraved with the phrase rendered as Destroyer of Demons, a tradition that began some time after the blade hidden inside the Yoriichi Type Zero was found.

Because the blades constantly soak up sunlight, beheading a demon with one kills it for good, the head and body crumbling to ash much as they would in daylight. Strikes to other parts of the body are far less effective, so decapitation remains the only reliable kill.

A blade shifts to a distinct color when its owner first draws it, though only if that owner has reached a certain level of skill. The color is tied to the Breathing Style the user suits best: black for Sun, blue for Water, red for Flame, yellow for Thunder, green for Wind, gray for Stone, and so on. Black blades are poorly understood and seen as an ill omen. Raising a blade's temperature enough turns it a glowing bright red, which suppresses demon regeneration and inflicts severe pain; this is achieved through Nezuko's Blood Demon Art, a powerful grip, or clashing two blades together with a Demon Slayer Mark active.

The swords are wielded throughout the Demon Slayer Corps. Tanjiro Kamado and Yoriichi Tsugikuni both carry obsidian-black blades, Giyu Tomioka a deep blue katana, the Rengoku line a red one, Zenitsu Agatsuma a yellow blade marked by a lightning motif, and Inosuke Hashibira a pair of serrated katanas. Swordsmiths of the Swordsmith Village forge each weapon from ore the recruit selects after passing Final Selection. The blade debuts in Chapter 6 of the manga and Episode 4 of the anime.