Bright Red Nichirin Sword

A **Bright Red Nichirin Sword** (赫刀, *Kakutō*?, ViZ. "Bright Red Blade"), known mostly as a **Bright Red Nichirin Weapon** (赫武器, *Kaku Buki*?) refers to the ability that turns a bladed Nichirin weapon bright red with special properties for a certain amount of time and is only accessible by Demon Slayers who have awakened the Demon Slayer Mark.

## Overview

Normally, Nichirin Swords and other bladed Nichirin weapons can turn into virtually any color dependent on the user and their Breathing Style. However, there is one color that cannot be normally accessed: a shining bright red. Unlike other colors, a bright red sword has special properties and can only be accessed by Demon Slayers who have awakened the Demon Slayer Mark. Moreover, any Nichirin sword can become bright red regardless of the blade's original color. However, the blade can only stay bright red for a certain amount of time before returning to normal.

The bright red hue that envelops the blade is achieved through deliberate actions intended to raise its temperature. This transformation is fueled by the conversion of mechanical energy into thermal energy. The following four distinct methods of activations are known:

1. **Friction**: Clashing two swords together with enough force that the friction generated between them produces a substantial heat buildup, causing both blades to illuminate in a bright red hue.
2. **Pressure**: Gripping a sword with an unwavering strength to exert immense pressure onto the metal surface. This focused pressure produces a localized heating effect, causing the blade to turn bright red.
3. **Ignition**: Engulfing a sword in flames with Nezuko Kamado's **Exploding Blood** and further heating it to raise its temperature to an extreme level. The searing heat of the flames or even the heated Reiki turns the sword bright red. These two are the only methods which doesn't require a Demon Slayer Mark.
4. **Reiqi Infusement & Heating:** When an Umoya infuses and coats their Qi around their or another individual's Nichirin Sword and further manipulating their Seiqi by heating it, the intense heat from the heated Seiqi both inside and around their blade turns the blade bright red to a much higher degree.

### Effects

   The most notable effect of a bright red Nichirin sword is its ability to hamper or even completely nullify a demon's regeneration. The bright red Nichirin sword also generates extreme heat, which can cause immense pain to demons and cause them to cough up blood. The extent of which a bright red Nichirin sword can hinder a demon's regenerative ability can be quite apparent, as seen with the likes of Hantengu and Muzan Kibutsuji himself taking around a dozen seconds to regenerate damage that would be healed instantly under normal circumstances.

Bright red Nichirin swords also seem to be able to nullify the regeneration of demons that have just been decapitated, thus permanently killing them even if they managed to regrow their heads after being decapitated by a Nichirin sword. This can be inferred when Kokushibo, who had just overcome his weakness of decapitation from Nichirin swords, slowly crumbled away and was unable to regenerate despite being stabbed in a non-lethal spot by a bright red Nichirin sword.

Yoriichi Tsugikuni's and Dumisani Mavundla's bright red Nichirin swords are the most potent out of all Demon Slayers, with Yoriichi's being able to burn on a cellular level and leave scars that even the Demon King himself can't heal even after centuries. Furthermore, once slashed by Yoriichi's Nichirin sword, the cells in the affected region will be continuously burned for centuries.

* For Dumisani's case, theirs are the same as Yoriichi's. They can make it higher by heating the already potent bright red sword with their Reiqi, making it more versatile than Yoriichi's blade, making it even capable of burning down to an atomic level as well. This was remarked by Yuzuriha Kijin when she was cut through the right side of her waist and having half of her neck cut through in her battle against the 1st Umoya King.

## Trivia

* While the current accepted reading of the Japanese name of the Bright Red Nichirin Sword is "Kakutō", it has also been rendered as "Shakutō" in the past.