The Sharingan

The Sharingan (写輪眼, The Sharingan? literally "Copy Wheel Eye," English "Mirror Wheel Eye") is an eye technique (瞳術, dōjutsu?) that naturally occurs in a select few members of the Uchiha clan. The Sharingan is thought to be descended from the Byakugan,[30] but grants the user different abilities and a different insight. The Sharingan does not automatically appear from birth in a user; instead, it will usually appear when the user is in a life-threatening situation, where the power of the Sharingan could save them. After this first appearance, the user can then activate the Sharingan any time they wish. The power of the Sharingan is judged through the number of tomoe in the eye, with a maximum of three in each. The characters that possess the Sharingan in the current Naruto storyline are Sasuke Uchiha, Itachi Uchiha, Madara Uchiha, and Kakashi Hatake.

The Sharingan's first and most well-known ability is to memorize any technique that it witnesses. It can memorize any standard form of jutsu with perfect accuracy, allowing the user to use the techniques as his own. In order to reproduce copied jutsu, however, one must have the necessary skill or ability to perform them.[31] Its second ability grants the user incredible clarity of perception, allowing them to track fast-moving objects with ease and even predict the subsequent movements of those objects.[32] This perception is great enough to see through genjutsu and to observe the movement and flow of chakra, but not to the same extent or clarity as the Byakugan.[33] The Sharingan's third capability is a unique brand of hypnosis that involves suggesting actions and thoughts to the opponent. When used in conjunction with the aforementioned aspects of the Sharingan, this allows the user to perfectly mimic every move their opponent makes, even before they do, making it appear as if the user can see the future.[34] It also allows for other forms of hypnotism, such as putting an opponent to sleep, replaying memories to someone else, creating various illusions to fool an opponent, or even controlling them.

It is possible to transplant Sharingan eyes from one person to another, as occurred with Kakashi and his deceased teammate Obito Uchiha.[35] However, transplanted eyes do not work as well in a non-Uchiha body; Kakashi's eye is always active, causing him great strain when he uses it and forcing him to recuperate for extended periods of time after a battle. Uchiha clan members are not burdened with this weakness; while activation of the Sharingan does consume chakra, the drain is so small as to be almost insignificant. Itachi in particular seems to have no trouble keeping his Sharingan activated near-constantly.