The black color of the blade symbolizes the powerful Sun Breathing Style in the demon slayer Corps. This breathing style was first created by the legendary demon slayer Yoriichi Tsugikuni, the strongest demon slayer to have ever lived. Both Tanjiro and Yoriichi wield this rare-colored sword. Although it is mentioned in Episode 5 of Demon Slayer, the black blade is often thought to bring misfortune to demon slayers, as those who have held it in the past have had a short lifespan.

Nichirin Swords Explained
Demon slayers use Nichirin Swords as their signature weapons. Craftsmen make these unique swords from a rare type of metal named scarlet crimson ore and scarlet crimson iron. These types of metals absorb sunlight and conceal it within the metal blade, allowing it to act as an alternative to sunlight to slay demons.
Furthermore, the metal that forms the basis of Nichirin Swords comes from “Sunlight Mountain,” placed close to the sun and bathed in its rays. This mountain is unique in that it is situated in a location that is immune to clouds or rain.

When a skilled swordsman crafts the Nichirin Sword and is given to a demon slayer, the color of the sword is said to reflect the wielder’s strengths and weaknesses. Different colors of Nichirin Swords are also associated with specific breathing styles; for example, Kyōjurō Rengoku’s blade is red because his combat style is flame breathing.
These swords are not only visually stunning but also incredibly powerful and capable of evolving and growing stronger as the wielder gains more experience and hones their skills. In the series, The Nichirin Swords are portrayed as highly durable weapons with the ability to slice through any demon. These swords play a central role in the series as demon slayers rely on them to protect humanity from the threat of demons.
Read more: Why Is Muzan Scared of Yoriichi in Demon Slayer?

The Meaning Behind the Colors of the Demon Slayer Swords
The colors of the demon slayer Swords carry significant meaning and serve as a visual representation of the wielder’s skills and abilities. Each color is associated with different breathing styles, as listed below:
COLOR | REPRESENTATION |
Black | Sun |
White | Mist |
Indigo-gray | Beasts |
Red | Flame |
Pink | Love |
Light Pink | Flower |
Amber | Sound |
Yellow | Thunder |
Green | Wind |
Lavender | Serpent |
Purple | Moon |
Blue | Water |
These colors help to differentiate between the members of the demon slayer Corps and provide insight into the unique strengths and abilities of each demon slayer.
Read more: Is Demon Slayer: Kimetsu No Yaiba Over?