Amaterasu

Amaterasu is a ninjutsu that uses the highest level of Fire Release. It is said to represent the, the antipode to Tsukuyomi — a genjutsu of similar power and a fellow Mangekyō Sharingan dōjutsu. Use of the technique puts a great deal of strain on the user, usually causing their eyes to bleed.

Overview
The jet-black flames of the Amaterasu, said to be "the fires from hell" are as burning hot as the sun itself. By focusing their vision upon an object the user is able to ignite the flames, kindle at the focus of the user's vision. Though the flames have been stated to be unavoidable, Amaterasu has been avoided a few times; Sasuke Uchiha managed to dodge the flames when Itachi tried focusing on him, though Itachi did not actually want to kill him and managed to hit Sasuke shortly after regardless, and A using his Lightning Release Chakra Mode enhanced Body Flicker Technique avoided a short-range Amaterasu launched at him by Sasuke in an instant.

Obito managed to save himself from the flames by some unknown means when he was hit by Sasuke, though indirectly. After becoming the jinchūriki of the Ten-Tails, he was able to defend himself with the Truth-Seeking Balls. When he was actually set ablaze with the black flames through a combo-attack of Sasuke and Naruto, he recovered through the healing abilities of the Ten-Tails.

The black flames of Amaterasu are stated to burn through mostly anything in their path, even smothering regular fire techniques with ease. Amaterasu is said to never stop burning; even when whatever is caught by Amaterasu is completely reduced to ash or destroyed, it can still continue burning for seven days and seven nights. It cannot be extinguished with water or any other normal methods. However, the flames cannot burn through chakra, as they failed to burn into or through Gaara's chakra-infused sand, while Naruto managed to prevent the flames from reaching his flesh with Kurama's chakra cloak. Sasuke used this to his advantage by coating the ribcage of his Susanoo for a defensive layer without harming himself or his spiritual guardian.

However, the flames burn fairly slowly compared to ordinary flames. This allows anyone struck by Amaterasu an opportunity to remove whatever clothing or body parts have been caught ablaze before the flames spread further. Nagato was able to deflect the flames from his body using Shinra Tensei. Jiraiya was also able to seal the flames with the Fire Sealing Method. Also, the Ten-Tails was able to remove the body parts from its body which set ablaze by Sasuke Uchiha. The flames can also be extinguished by the user that summoned them, albeit it puts great strain on their eyes.

Although this technique can be performed without using hand seal, Sasuke casted Amaterasu on Kaguya by using tiger hand seal, which he normally uses for his fire release techniques.

Manipulation
Users of this technique have shown the ability to manipulate these flames to some extent. Itachi was able to quell the flames during his battle with Sasuke, something as Zetsu noted was done to protect Sasuke's eyes. Sasuke himself would later quell the flames during his battle with Killer B, after Karin had accidentally been caught in the flames. Furthermore, the Uchiha derived an ability known as Blaze Release: Kagutsuchi through which they could manipulate the flames to serve as not only an offensive ability but a defensive one as well.

Influence
As from the ancient Japanese myth and religion of Shintō, Amaterasu, Tsukuyomi, and Susanoo are all gods. When Izanagi washed his face after escaping the underworld the Sun Goddess, Amaterasu, was born from his left eye.