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.

In order to fight the demons, they use weapons called Nichirin blades, which are made with Scarlet Crimson, Iron Sand, and Scarlet Crimson Ore, which are all constantly exposed to sunlight, and are collected from the mountains. Seen as they have absorbed sunlight, when the swords are used to kill a demon, they stay permanently killed. When they are decapitated, their bodies turn to ash, although the swords are less effective if used on other parts of the demon's body.

The swords are also sometimes referred to as Color Changing Katanas; this is because when first drawn by its owner, they display a color, which only appears if the owner has presented a certain level of demon fighting skills. The swords come in a variety of colors and in the Japanese show, each color has a different meaning and symbolizes something unique, so let's take a look at each sword color and what they mean.

Amber

The color amber represents sound and is the color of The Sound Hashira. Tengen Uzui's Nichirin's uses cleavers that are connected by a chain, which is a perfectly loud weapon. It is also the color of energy, which comes from Tengen as he swings his cleavers with force and powerful energy to defeat his enemies. He is not afraid of making his appearance always known and can easily cause loud chaos.

White

White blades symbolize mist. There is no other demon slayer like Muichiro Tokito, who is light, airheaded and slick. His mist breathing technique is inspired by the breath of wind and is associated with staying calm and collected like a gentle breeze - the perfect attitude to stay calm when defeating a demon.

Green

The emerald green blade also represents wind breathing and is seen by Wind Hashira, Sanemi Shinazugawa. The abilities that come with his green sword is being fast like a tornado whilst also staying extremely calm. He can also be violent and furious like a hurricane, and any demon that gets in his way does not stand a chance.

Black

Black is the most mysterious color of all the blades, and is held by the main character, Tanjiro. It is a rare blade and represents the sun; it also holds a theory that the demon slayers who own this sword are not to live a long life. Black swords are also supposed to hold all the colors, which means Tanjiro is to find his way through all colors and breathing techniques. It is also said to absorb the most sunlight, so it is the strongest sword against the demons.

Blue

Blue is the color for water, and is one of the first blades that is shown to us in the series. Giyu Tomioka, the Water Hashira uses the breath of water technique to defeat the demons, which makes his movements fluid, fast and seem effortless like slow ripples in the water, and is able to kill demons in one smooth swish of his blade, making him one of the most respected demon slayers.

Red

Red is a threatening color and symbolizes fire and flames. Kyojuro Rengoku uses a red blade and is dangerous, eccentric, and strong, practicing the breath of flames technique to make him powerful and fierce. His strength, both without and within, makes him a brilliant demon slayer, as he is tough, fiery and burns with power when killing demons. His sword is also unique, as it is styled with a decorative flame that runs down his blade.

Yellow

Yellow represents thunder, and is used by Zenitsu Agatsuma. He is as fast as lightning, and strong and powerful like a thunderstorm, which you could not guess by his shy personality and low self-esteem. Although, when he is needed, he explodes and can kill a demon easily. Much like the red blade, his sword is patterned with a lightning bolt that runs down the blade, so he might be shy, but his sword is powerful.

Gray

Gray can symbolize that the holder will master the stone breathing technique, but also that they may not pull a traditional blade. Gyomei Himejima, the Stone Hashira, for example, instead of wielding a sword, holds a giant axe attached to a chain which is still awesome, much like amber. Stone breathing is linked to being able to detach from emotions and be strong and steady, even though Gyomei is emotional and gentle. Yet, he can easily turn it off and become strong, threatening and intimidating when he needs to be.

Pink

Pink of course represents love, and is related to the breath of love technique. Mitsuri Kanroji holds the pink blade and her passionate personality really shines through. Mitsuri even created the love breathing technique, as her muscles are much more dense than normal, which means that she is strong but flexible and dances around killing demons very passionately.