Tanjiro Kamado, the main character of the "Demon Slayer" series, wields a sword called Nichirin Blade, which has a black blade. The black color of Tanjiro's sword holds a special significance within the story:

1. Sun Breath Technique: Tanjiro practices the Sun Breath technique, a unique swordsmanship style passed down through his family. The black blade of his Nichirin Blade represents the use of this technique. In the "Demon Slayer" universe, each practitioner of the Sun Breath technique has a different coloration on their blade. Tanjiro's black blade signifies his mastery of the Sun Breath style.
2. Dance of the Fire God: Tanjiro's black-bladed sword is further connected to his family's ancestral technique known as the Dance of the Fire God. This technique combines breathing techniques, swordsmanship, and the elemental power of fire. The black blade represents the connection to this powerful and ancient technique.

It's important to note that the black coloration of Tanjiro's sword is specific to the fictional world of "Demon Slayer" and serves as a visual representation of his unique abilities and lineage. In reality, traditional Japanese swords, such as katanas, are typically not made with black blades.