Itachi Uchiha

Itachi Uchiha was an ANBU Captain from Konohagakure's famed Uchiha clan. He would later become an S-ranked missing-nin after murdering his entire clan in what would become known as the Uchiha clan massacre, and defected from the village. He later joined the criminal organisation Akatsuki where he was partnered with Kisame Hoshigaki.

A child whose genius manifested at a young age, Itachi's teachers at the Academy noted that his progress hardly required any help, having been quickly promoted through the ninja ranks while still a child, further showing his remarkable capacities. In his battles, Itachi was shown to be an immensely powerful ninja and gained praise from allies and foes alike. During his battle against Kakashi Hatake, Kurenai Yūhi, and Asuma Sarutobi, Kakashi commented that Itachi was not fighting with even half his strength. Tobi has also stated that Itachi never ceased to amaze him. Despite his own impressive abilities, Itachi never underestimated his opponents, given his praise of Jiraiya, in which he noted to Kisame that, provided he had the latter's help, if he fought Jiraiya, they would either kill each other or Itachi himself would lose.

Tsukuyomi is noted to be one of the most powerful genjutsu in existence. It is unique to the Uchiha clan and only those who have awakened the Mangekyō Sharingan can perform it. It is said to represent the "Spiritual World and Darkness" (Seishinkai to Yami), the antipode to Amaterasu — a ninjutsu of similar power.

Tsukuyomi requires eye contact to be performed, trapping the target within an illusion completely under the user's control. Itachi's prowess with the technique has allowed him to alter the perception of time with ease within the genjutsu to make a few seconds seem like many days as a means to torture the target. This results in the victim suffering psychological trauma that incapacitates them for a considerable period of time. After Itachi used it on Kakashi in Part I, Kisame was surprised that Kakashi's mind was still intact. Only Tsunade has been shown capable of curing this psychological damage.