All Sharingan Contacts
A Mangekyō Sharingan is distinguished from a normal Sharingan by its appearance, which changes the form of the tomoe seal. The exact design differs for each user, though all resemble pinwheels. It is initially awakened by the trauma suffered from witnessing the death of someone close to the user. Uchiha have historically misunderstood this criteria as the user needing to be responsible for the person's death, and for that reason they developed the practice of killing their closest friends in order to gain the Mangekyō Sharingan. Obito's Mangekyō activated immediately after his trauma, whereas, in Naruto Jinraiden, Sasuke's Mangekyō didn't activate until several weeks afterwards.
The Mangekyō Sharingan retains all of the Sharingan's generic abilities, such as casting genjutsu and the ability to distinguish chakra. In addition to these, the Mangekyō grants powerful abilities that differ from user to user, though abilities may be similar in nature; both Sasuke and Itachi have access to Amaterasu's flames, though the extent to which they can use them differ. The abilities of a Mangekyō Sharingan may not even be the same for both of a single user's eyes, as Itachi has Amaterasu in one eye and Tsukuyomi in another. Once a user awakens the Mangekyō in both eyes, or the ability of both of their eyes, they are able to perform Susanoo.
The Mangekyō Sharingan's abilities drain a considerable amount of chakra when performed. Its usage and activity also place a great strain on the user themselves, wearing at the user's body and causing deterioration to their vision until eventually over-usage leaves them blind. Their vision can be restored by receiving the transplanted Mangekyō of an Uchiha with strong blood ties — ideally a sibling — thus awakening so-called Eternal Mangekyō Sharingan (永遠の万華鏡写輪眼, Eien no Mangekyō Sharingan). The Eternal Mangekyō merge the designs of the transplanter and the transplantee's original Mangekyō. Their Mangekyō-based abilities are made stronger and they no longer suffer any negative side-effects from the usage. According to Madara, the Eternal Mangekyō Sharingan is proof an Uchiha continues to seek something despite experiencing great losses.Should the eyes evolve to this state, the user will retain all their previous techniques from their original eyes. In addition to the unique techniques, the "straight tomoe" (直巴, Choku Tomoe) form of Madara's and Sasuke's Eternal Mangekyō Sharingan grants them fluidity in their movements when fighting.
As with any dōjutsu, Mangekyō Sharingan can be transplanted into non-Uchiha, granting them all its abilities albeit with steeper chakra demands. Abilities of a Mangekyō Sharingan can also be programmed to activate under certain circumstances, either within the user's own eyes or in a target of the user's choosing; this programming remains even after death.
The Mangekyō Sharingan also grants its user the ability to read and decode the Uchiha Clan's Stone Tablet. According to Obito, the Mangekyō Sharingan can decode it more than the Sharingan, but less than the Rinnegan.