Nichirin swords are the main weapons used by Demon Slayers in the Demon Slayer Corps in order to kill demons. They are forged with Scarlet Crimson Iron Sand and Scarlet Ore, both of which are found on high mountains like the Sunlight Mountain, which is perpetually bathed in sunlight all throughout the year on Mount Yoko.

As they constantly absorb sunlight, decapitating demons with Nichirin Swords can permanently kill them. Once their neck-bone is slashed by the weapon, their heads and bodies disintegrate into ash in a similar fashion to when exposed to sunlight. However, Nichirin Swords are less effective when used to slash other parts of a demon's body, making beheading the only viable option for Demon Slayers.

Nichirin Swords take on a distinct color when first drawn by its owner, which is why they are also referred to as "Color Changing Katanas". However, the holder is required to have a certain amount of skill, or the blade will not change color.

Demon Slayer recruits choose their own ore after successfully passing the Final Selection. The ore will then be used by a swordsmith of the Swordsmith Village during the forging process, and the swordsmith will personally bring the weapon to the Demon Slayer.

After the Demon Slayer reaches the rank of Hashira, their weapons will be engraved with the words "Destroyer of Demons" (惡あっ鬼き滅めっ殺さつ). This tradition came from the creation of the sword that Tanjiro and Kotetsu found inside the Yoriichi Type Zero, which was created for the sole purpose of annihilating demons.

Swordsman

Tanjiro Kamado(Tanjiro Sword)

• A standard sized and shaped Nichirin katana that is obsidian black in color.
• A black ring connected to its core by lines with a border of the same color. It heavily resembles a wagon wheel in appearance.

Sakonji Urokodaki

• A standard sized and shaped Nichirin katana that is dull gray in color.

Zenitsu Agatsuma(Zenitsu Sword)

• A standard sized and shaped Nichirin katana with a lightning streak along its blade.
• Circular shaped with 4 slight indentations, the center has a silver tone with small triangles and has a golden border.

Inosuke Hashibira(Inosuke Sword)

• A pair of standard sized Nichirin katanas chipped with numerous gashes within the blade's edge that is indigo-gray in color with no handguard.
• A black ring connected to its core by an arrangement of semicircles, possibly to resemble a fish.

Kanao Tsuyuri(Kanao Sword)

• A standard sized and shaped Nichirin katana that is light pink in color.
• Circular shaped with a light pastel blue center and border, filled 3 red sakura flowers and a winding pattern that is light green in color.

Genya Shinazugawa

• A western double-barreled shotgun with Nichirin bullets.
• A shorter and smaller Nichirin wakizashi that are dull gray in color.
• Two hollow ovals that overlap its core and are a dull shade of brown.

Giyu Tomioka(Giyuu Sword)

• A standard sized and shape Nichirin katana that is deep blue in color.
• Hexagonal shaped with a bronze core and with an overlapping fuschia border.
• Tomioka's second blade obtained during the fight against Muzan has a handguard resembling a whirlpool.

Shinobu Kocho(Shinobu Sword)

• A sword with a thin blade and a needle-like tip that is lavender-blue in color.
• Shaped like a butterfly: Each wing has an aqua colored core with an orange border.

Kyojuro Rengoku(Rengoku Sword)

• A standard sized and shaped Nichirin katana with a red flame pattern along its blade.
• Shaped like a flame with a red core and an orange border.

Tengen Uzui

• Two massive Nichirin cleavers connected by a chain that is amber in color.
• Circular shaped with 4 slight indentations and gold in color, there's a maroon ring that connects to the center; it has an outer teal border.

Muichiro Tokito

• A standard sized and shaped Nichirin katana that is white in color.
• Rectangular shaped with hollowed rectangles at each corner.

Mitsuri Kanroji(Mitsuri Sword)

• A long whip-like nichirin sword that is pink in color.
• Shaped like a 4 leaf clover; The leaves are heart-shaped with a pink core and a golden border.

Obanai Iguro

• A serpent-like Nichirin katana that is lavender in color.
• Gold circular shape engraved with two snakes connected by several plant-like patterns.

Sanemi Shinazugawa(Sanemi Sword)

• A standard sized and shaped Nichirin katana that has a jagged jaw-like pattern that is green in color along its blade.
• Abstract shape with 8 points with an overlapping pattern; Each plate has a forest green core with a silver border.

Gyomei Himejima

• A Nichirin spiked flail and battle axe connected by a long chain that is dull gray in color.

Yoriichi Tsugikuni

• A standard sized and shaped Nichirin katana that is usually obsidian black in color, but bright red when in battle.
• Circular shaped with 4 slight indentations, with a black center and a golden border.