Mangekyō Sharingan

Mangekyō Sharingan is an advanced form of the Sharingan that has only been activated by a handful of Uchiha. It was also awakened by Kakashi Hatake — a non-Uchiha through unknown means.

Overview
The Mangekyō Sharingan has the ability to control the Nine-Tailed Demon Fox, although Madara Uchiha is the only one to accomplish this milestone, Tobi has done the same but seemingly with only a regular Sharingan. 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 the Sharingan, the appearance of the Mangekyō Sharingan differs from user to user; for example, Itachi Uchiha and Kakashi Hatake's resembles a pinwheel, and Sasuke Uchiha's looks like three intersecting ellipses.

The Mangekyō Sharingan is acquired through the trauma experienced from the death of the person closest to the Sharingan user. With the user normally having to witness or experience this first hand, Uchiha throughout history have killed the person closest to them in order to expedite this process, though how Kakashi and Shisui gained their respective 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.

Over time, use of the Mangekyō Sharingan's techniques deteriorates the user's eyesight to the point of blindness. Only by taking and transplanting the Mangekyō of another Uchiha clan member can the vision be restored, a process that results in the creation of an  Eternal Mangekyō Sharingan. The tighter the blood ties are between the "donor" and the receiver, the better it is for compatibility — a sibling for example would make the best donor. The time from fusing the donor's Mangekyō with the receiver's Mangekyō to the point of full recovery is at least several days as seen in Sasuke's case. Not only does this process permanently restore one's eyesight, but it also gives the person even greater power. The Eternal Mangekyō Sharingan also changes form from the original Mangekyō form, to what appears to be a fusion of the wielder's own Mangekyō with the transplanted one.

Through unknown means, the Eternal Mangekyō Sharingan can also evolve even further into the Rinnegan, as witnessed by Madara Uchiha's usage of the dōjutsu, which he claims to have awakened shortly before his death.

Itachi Uchiha
Itachi Uchiha gained the Mangekyō Sharingan by aiding his best friend, Shisui in killing himself. With the Mangekyō Sharingan, Itachi was able to use at least three powerful techniques. 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 Spell 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 known techniques was Susanoo, which allowed Itachi to summon a massive ethereal warrior. This entity fights on behalf of Itachi and shields him from most attacks. According to Zetsu, when it is combined with the Yata Mirror and Sword of Totsuka it essentially made Itachi invincible. Itachi's Susanoo has three forms which it goes through; an incomplete skeletal form, a complete warrior-like form and a final form that resembles a yamabushi.

Use of the Mangekyō Sharingan put a great strain on Itachi's body would quickly deplete his chakra reserves, to the point that after using it three times in a day he deactivated his normal Sharingan. By the time he battled Sasuke, his sight had been reduced to a large blur, yet having resolved himself to dying at the hands of his brother, pushed past this limitation and used his Mangekyō Sharingan more than three times as well as other techniques. A clone containing 30% of his chakra couldn't use it once (though this may be attributed to Itachi's below average stamina). After Itachi's death, Sasuke, at first, refused to take his eyes, but eventually did to escape the 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 spell called Kamui to send a target to another dimension. The attack requires considerable effort to aim with precision, leaving Kakashi's chakra significantly drained; considering that Kakashi is a non-Uchiha, the chakra drain is more significant to him than the other users of the Mangekyō Sharingan. When he first used the technique, he collapses after using it three times in a single day and had poor control at aiming it. However, after much practice with his Mangekyō, he can control the size of it to only affect the target and use precise aim to hit speeding targets. He can also use it twice in quick succession, without showing immediate chakra drain and fatigue, 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 like a combination of both his and Izuna's Mangekyō.

Madara became one of the few to awaken Susanoo, as a result of awakening Amaterasu and Tsukuyomi in both eyes. His Susanoo has shown unique attributes in that it has two faces and two sets of hands instead of a single face and three hands as seems to be the standard. Madara can also completely control the Nine-Tails with the Mangekyō Sharingan, a feat which no other Sharingan user besides Tobi managed.

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 Tobi, Izuna willingly gave up his eyes for the Uchiha clan's sake, however Itachi implied that Madara took them by force.

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 own 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, but in an inverted manner. With his "right Mangekyō" he can use Tsukuyomi to break a target's will and paralyse them. Danzō Shimura stated that Sasuke's version is not yet capable of altering the victim's perception of time, and thus is vastly inferior to Itachi's. 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, creating the Blaze Release, 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 defence 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. Sasuke's Susanoo appears more demonic than Itachi's.

Due to having much larger chakra reserve than his elder brother, Sasuke can use the Mangekyō Sharingan techniques more than three times a day. While Itachi was critically exhausted after using Tsukuyomi and Amaterasu once each, and then Susanoo as a last resort technique that ultimately led to his death, Sasuke could maintain Susanoo for extended periods of time, on top of using the Amaterasu and Tsukuyomi several times a day along with some other chakra-consuming techniques like the Chidori. Regardless, like Itachi, using the Mangekyō Sharingan puts a great strain on Sasuke's body and eyes.

Initially, Sasuke refused to transplant Itachi's eyes to restore his vision even when it was reduced to a heavy blur at best, claiming that his views were different from Itachi. However after meeting Naruto again and shocked at his determination to save Sasuke from his darkness, Sasuke decided to take Itachi's eyes so he could kill Naruto with his full strength. His Eternal Mangekyō Sharingan takes the shape of his old Mangekyō Sharingan but incorporates a straightened version of Itachi's Mangekyō Sharingan design into the centre. His new eyes produce a more ghostly-shaped Susanoo. It is also able to condense Amaterasu and lock on multiple targets at once.

Shisui Uchiha
Shisui Uchiha acquired his Mangekyō Sharingan at some point in time through unknown means. It granted him the ability to cast powerful genjutsu spell, the most powerful of his genjutsu arsenal being Kotoamatsukami. This spell allowed him to manipulate an opponent's thoughts without them having the slightest idea that they were being controlled. The only drawback of using that technique was the fact that it would render his Mangekyō unusable for quite some time without aide. A highly coveted ability, Shisui's right eye was stolen by Danzō Shimura while he was still alive. Shisui entrusted his left eye to Itachi Uchiha and told him to protect the village; Itachi implanted it into a crow and stored it inside Naruto Uzumaki. He then made it appear as though he had crushed his own eyes in order to prevent a feud over his eyes and erased his existence, though it was thought that he was drowned by Itachi in the Naka River. When activated, Shisui's Mangekyō Sharingan has four points which go around in a circular, saw-like motion. Both eyes are eventually destroyed, with Danzō crushing his before dying and Itachi incinerating the crow after it came back out of Naruto.

Spells
Amaterasu Blaze Style Magatama Blaze Style: Kagutsuchi Kamui Kotoamatsukami Meteorite Technique Shield of Black Flames Susanoo Tsukuyomi Yasaka Magatama

Trivia

 * In the anime, in the fight against A, the internal intersection lines of Sasuke's Mangekyō Sharingan are replaced by a circle.
 * In the anime, when Kakashi used his Mangekyō Sharingan to warp away Sasuke's Susanoo's arrows, the black and red colours became inverted.