Amaterasu

This Mangekyo Sharingan ninjutsu is an unquenchable black flame ignited within the caster’s line of sight. It is the highest level of Fire Release with flames far hotter than what ordinary fire jutsu can accomplish even by the strongest shinobi and likened to the heat of the sun itself.

Amaterasu will burn for seven days and nights or until its target has turned to ash. Its incredible heat and undying flames means that it is quite capable of burning or melting its way through practically any substance given time. Even fire itself can be burned out by the superior Amaterasu.

It cannot be extinguished through normal means and does not require fuel for it to burn, so any volume of water will simply evaporate and depriving it of oxygen would have no effect. But when it interacts with something flammable, the black flames are quick to spread so that even a small fire can turn into a firestorm that rages for days.

When a human is set alight, it can take only seconds for them to be completely enveloped in flames and rendered defenseless from the heat and pain, requiring mental fortitude and quick thinking to avoid such a fate.

Unlike ordinary fire jutsu, these black flames will ignite specifically at the target within the caster’s sight without traveling the intervening space. They can continually create this fire anywhere within their line of sight even while shifting their gaze, allowing the flames to spread under their direction.

The only way for an enemy to overcome Amaterasu is to absorb the flames or seal them away. Otherwise they would need to intercept the flames with some kind of defence, move to avoid being set alight or remove the burning material before their flesh is caught alight. The caster, however, has the innate ability to extinguish Amaterasu to prevent it from going out of control.

Kagutsuchi

This Mangekyo Sharingan ninjutsu is the ability to freely apply shape transformation to any and all flames within the caster’s sight.

When they perform their regular fire ninjutsu, they can control these jutsu beyond their normal limits to make them move and change in all kinds of unpredictable ways that would be supremely difficult to manage otherwise. Such as turning a fireball into a mass of burning spikes, a flamethrower into a wall of flame or a fiery dragon into a swirling vortex. More importantly, the caster can accomplish the same effects on the fire jutsu of others which allows them to deflect incoming flames to protect the allies or turn them back upon their enemies.

But the true potential of the jutsu is realised when used in conjunction with Amaterasu as they directly complement one another, allowing the caster to go far beyond merely igniting and extinguishing the black flames.

This control can make the fire function like a solid mass to interact with other substances in ways that it ordinarily cannot. It can be shaped into spikes to pierce through an object, expanded into a shield for protection or shot like arrows to strike from a distance. The flames can even be held in the caster’s hand without burning them by preventing the flames and heat from affecting them.

Uchiha Sasuke, the latest among those to have awakened these two jutsu , chose to call this combination “Blaze Release” and proved the oustanding potential of the style by wielding it with the weapons of Susano’o once he awakened an eternal Mangekyo Sharingan.