Amaterasu

Name: Amaterasu (天照, Illuminating Heaven) Type: Kekkei genkai, Offensive Users: All Mangekyou Sharingan users

Amaterasu is one of the most powerful ninjutsu, opposite of Tsukuyomi, one of the most powerful Genjutsu. Amaterasu is unique to Itachi Uchiha, who later gave the power to Sasuke Uchiha. The jet-black flames are said to be as hot as the sun, and will burn for seven days and seven nights. Since the Mangekyo Sharingan is necessary to activate this jutsu, not many have learned it. All that is known is that it is very powerful since it can punch through a Mountain Toad's stomach which is, as stated by Jiraiya, fire retardant. Not surprisingly, it appears to use a large amount of chakra. Though stated in the databook to burn everything reflected on its retina; Zetsu also commented that the Amaterasu burns everything within Itachi's wide field of vision to cinders with an unholy black flame, to the degree of being able to burn an entire forest or village with it.

During the battle between Itachi and Sasuke, after Sasuke escaped Tsukuyomi all Genjutsu used in the battle between the brothers became pointless. Itachi was forced to shift from his most powerful illusion to his most powerful ninjutsu. As opposed to Tsukuyomi which originates in Itachi's left eye, the Amaterasu comes from his right eye. Although not shown in it's entirety when used while escaping Jiraiya in the battle with Sasuke either through fatigue or deterioration of his Sharingan, Itachi's eye was strained to the point that his drew tears of blood while executing the Amaterasu.

When Sasuke met Madara Uchiha, Itachi's Mangekyo Sharingan automatically used Amaterasu. Madara later explained that Itachi had somehow "programmed" an Amaterasu in Sasuke's eyes to detonate upon seeing Madara's Sharingan. Sasuke uses his own Amaterasu while fighting Kirābī, but uses his left eye as opposed to Itachi using his right. Like Itachi's, his eyes begin to bleed as well. After Karin is accidentally hit with Amaterasu, Sasuke uses his right eye to suppress the flames, and does the same with Kirābī.