Mangekyō Sharingan

The Mangekyō Sharingan is a heightened form of Sharingan.

Overview
The Mangekyō Sharingan allows the user to control the Nine-Tailed Demon Fox, although Madara Uchiha is the only one to accomplish this milestone. It also grants them access to other powerful techniques. The Mangekyō Sharingan is distinguished from a normal Sharingan by its appearance, which changes the form of the tomoe seal. Unlike in the case of the Sharingan, the appearance of the Mangekyō Sharingan differs from user to user; Kakashi Hatake's and Itachi Uchiha's both resemble pinwheels, Madara Uchiha's and Izuna's look more like a detailed form of the basic three-tomoe Sharingan, and Sasuke Uchiha's looks like three intersecting ellipses.

The Mangekyō Sharingan is acquired through the death of the person closest to the Sharingan user. To expedite this occurrence, Uchiha throughout history have killed their closest friends in order to meet this criteria, though how Kakashi gained his Mangekyō Sharingan has yet to be explained. To obtain the Mangekyō Sharingan, one must feel the emotion of losing a friend or family, as merely killing them or watching them die will not activate it.

Upon awakening, the Mangekyō Sharingan will deteriorate the user's eyesight, until the user's Sharingan is sealed forever and they are rendered blind. Usage of any of the Mangekyō Sharingan techniques will accelerate the blindness. Only by taking and transplanting the eyes of a sibling can the vision be restored, a process that results in the creation of the. Not only does this process restore one's eyesight and ensure that the light will never leave the eyes again, but it also gives the person greater power. The Eternal Mangekyō Sharingan also seems to change form from the original, with what appears to be a fusion of the current owners Mangekyō with the previous owners.

Itachi Uchiha
Itachi Uchiha gained the Mangekyō Sharingan by killing his best friend, Shisui. With the Mangekyō Sharingan, Itachi was able to use at least three powerful jutsu. With his "left Mangekyō" he could use Tsukuyomi, an extremely powerful genjutsu that allowed him to torture opponents for what seemed like days in a matter of seconds. With his "right Mangekyō" he could use Amaterasu, a ninjutsu which creates virtually-inextinguishable black flames at the user's focal point that continue to burn until the target is reduced to ash. The last of these techniques was Susanoo, which allowed Itachi to summon a massive ethereal warrior. This entity fights on behalf of Itachi and shields him from all attacks, rendering Itachi essentially invincible.

Use of the Mangekyō Sharingan put a great strain on Itachi's body and would quickly deplete his chakra reserves, as such he could only use it three times per day before becoming exhausted to the point where he couldn't use his normal Sharingan. A clone containing 30% of his chakra couldn't use it once. He told Sasuke that he wanted to take his eyes in order to escape these side-effects. After Itachi's death, Sasuke, at first, refuses to take his eyes, but eventually does so to escape the same side-effects and obtain an Eternal Mangekyō Sharingan.

Kakashi Hatake
Kakashi Hatake developed his own Mangekyō Sharingan during the time-skip. How he developed this is still unclear. With his Mangekyō Sharingan, Kakashi can use a space-time ninjutsu called Kamui to send a target to another dimension. The attack required considerable effort to aim precisely and left Kakashi's chakra significantly drained; he collapses after using the technique three times in a single day when he first used it. However, after greater practice with his Mangekyō, he could use it twice in quick succession without showing immediate chakra drain and fatigue, near instantly to counter Sasuke Uchiha's Susanoo arrows.

Madara Uchiha
Madara Uchiha was the first Uchiha to awaken the Mangekyō Sharingan. He eventually grew blind from overusing it, and only by taking his younger brother, Izuna's, eyes did he regain his sight. This also gave him an "eternal" Mangekyō Sharingan that gave him great power. His Eternal Mangekyō Sharingan looks identical in appearance to Madara's first Mangekyō combined with Izuna's Mangekyō.

Madara, posing as Tobi, has been shown using an unnamed space/time ninjutsu which makes him nearly invulnerable. He can also teleport himself or others to another location. It is unclear if either ability is because of his Mangekyō Sharingan. While it is unknown what other (if any) Mangekyō jutsu he may have, Madara has demonstrated detailed knowledge and understanding for each Mangekyō jutsu.

Izuna Uchiha
Izuna Uchiha acquired his Mangekyō Sharingan soon after Madara did. Madara later took Izuna's eyes to regain his lost vision. According to Madara, Izuna willingly gave up his eyes for the clan's sake.

Sasuke Uchiha
Sasuke Uchiha awakened his Mangekyō Sharingan after learning the truth about his brother, Itachi. In his grief over the knowledge that Itachi was not the villain he imagined him to be, coupled with Sasuke's role in Itachi's death, he awakens his Mangekyō Sharingan. Unlike other Sharingan, which have a black design and red background, Sasuke's Mangekyō is the first one that is shown to have a red design and a black background.

Sasuke has been shown using the same Mangekyō Sharingan abilities as Itachi. With his "right Mangekyō" he can use Tsukuyomi to break a target's will and paralyze them. Danzō Shimura stated that Sasuke's version is not capable of altering the victim's perception of time, and thus is vastly inferior. With his "left Mangekyō" he can use Amaterasu. It has been implied that his skill with Amaterasu surpasses Itachi's, as he is able to apply Shape Transformation to the flames, and even extinguish them. Sasuke has displayed the ability to use Susanoo, which he can even partially manifest to fit the situation, such as using a ribcage for defense or manifesting only an arm to interact with his surroundings. Sasuke's Susanoo develops in stages during various battles; he first starts using an incomplete version against the Fourth Raikage, develops a version capable of firing arrows while fighting with Danzō, and later forms a version almost identical to Itachi's during his battle with Kakashi.

Like Itachi, using the Mangekyō Sharingan puts a great strain on Sasuke's body and eyes. When he eventually starts to go blind, he has Itachi's eyes transplanted to restore his vision. His "Eternal" Mangekyō has yet to be seen, but he claims he can feel Itachi's power flowing through him.