A Nichirin Blade is a fictional weapon featured in the manga and anime series called "Demon Slayer: Kimetsu no Yaiba." Created by Koyoharu Gotouge, the series is set in a world where demons exist, and the protagonist, Tanjiro Kamado, becomes a demon slayer to avenge his family and protect humanity.

The Nichirin Blade is a special sword used by demon slayers to battle and kill demons. It is forged from a unique metal called Nichirin, which is derived from the Sun itself. The blades are designed to amplify the wielder's abilities and are highly effective against demons due to their specific composition.

Each Nichirin Blade possesses a distinct color, which corresponds to the unique abilities and personality traits of the demon slayer who wields it. The blade's color is determined by the user's "Breathing Style," a technique that involves controlling one's breathing to enhance their physical and mental capabilities.

Additionally, the blades have another significant characteristic: they emit a faint, constant glow, reminiscent of the sun. This glow intensifies when the sword is drawn and used in battle. It serves as a symbol of the demon slayers' mission to eliminate demons and protect humanity from their malevolence.

In the series, the Nichirin Blades play a vital role in the demon slayers' fights against demons, and each wielder's bond with their blade becomes an essential aspect of their character development.