Itachi
Uchiha
Mangekyō Sharingan
Sharingan
The Sharingan (写輪眼; Literally meaning "Copy Wheel Eye", Meaning (Viz) "Mirror Wheel Eye") is a dōjutsu kekkei genkai, which appears in some members of the Uchiha clan. It is one of the Three Great Dōjutsu (三大瞳術, San Daidōjutsu; Literally meaning "Three Great Eye Techniques"), along with the Byakugan and the Rinnegan. The Sharingan is also called "Heaven's Eye" (天眼, Tengan), because of the many abilities it grants the user.
The Sharingan's abilities consist of two parts: the "Eye of Insight" (洞察眼, Dōsatsugan) and the "Eye of Hypnotism" (催眠眼, Saimingan). The first of the Sharingan's powers is being able to see the flow of chakra. The Sharingan itself gives color to chakra, allowing the wielder to differentiate them.
Sharingan's second-most prominent ability grants the user an incredible clarity of perception, allowing them to easily recognize genjutsu and different forms of chakra, though not to the same extent as the Byakugan. This also allows the user to pick up on subtle details, enabling them to read lip movements or mimic something like pencil movements.
The Sharingan's third and most well-known ability is that it grants the user the ability to copy almost any technique that he or she witnesses, apart from other kekkei genkai techniques. The user can memorise ninjutsu, genjutsu, and taijutsu with near-perfect accuracy, allowing the user to use the techniques as their own, or even modify them to create their own new techniques. However, one must have the necessary skill or ability to perform them.
The Sharingan's final commonly-used ability is capable of inducing a unique brand of hypnosis that involves suggesting actions and thoughts to the opponent through genjutsu cast by simple eye contact between both parties. More advanced Sharingan users can take the hypnosis ability even further to the point where a powerful summon like Manda or even a tailed beast may be controlled.
Although the Sharingan consumes the user's chakra while active, the chakra levels that the user must exert are so insignificant that they can keep it active constantly. In fact, Itachi Uchiha is so masterful with the Sharingan that he is able to keep it active for most of the time, only once deactivating it after using Tsukuyomi on Sasuke and Kakashi, as well as Amaterasu to escape Jiraiya, due to exhaustion. However, when a Sharingan is transplanted to a non-Uchiha, the chakra drain is significant, leading them to cover it up when not in use. This seems to be circumvented by acquiring Senju cells in order to boost their vitality.
The Mangekyō Sharingan (万華鏡写輪眼; Literally meaning "Kaleidoscope Copy Wheel Eye"), noted to be the "heavenly eyes that see the truth of all of creation without obstruction," 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.
The Mangekyō Sharingan has the ability to control the Nine-Tailed Demon Fox and grant the user 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, Kakashi Hatake and Tobi's resembles a pinwheel, and Sasuke Uchiha's looks like three intersecting ellipses.
Itachi Uchiha gained the Mangekyō Sharingan by aiding his best friend, Shisui, in killing himself as the only way to get this Sharingan is through the trauma experienced from the death of the person closest to the user. However, it is unclear to this day how Shisui gained his Mangekyō Sharingan. With the Mangekyō Sharingan, Itachi is able to use at least three powerful techniques. With his "left Mangekyō" he can use Tsukuyomi, an extremely powerful genjutsu that allows him to torture opponents for what seem like days in a matter of seconds. With his "right Mangekyō" he can 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 known techniques is Susanoo, which allows 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 puts a great strain on Itachi's body and will quickly deplete his chakra reserves to the point that after using it three times in a day, he deactivates his normal Sharingan.
