THE SHARINGAN

The Sharingan is an eye technique that naturally occurs in a select few members of the Uchiha clan. The Sharingan is thought to be descended from the Byakugan, 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 call up 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, Kakashi Hatake, and Madara Uchiha.

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. A prime example is Rock Lee's taijutsu. While Sasuke was able to copy some of Lee's moves, they put a much more significant strain on him since he hasn't had the same training as Lee has.

The Sharingan's second ability is granting the user incredible clarity of perception, allowing them to track fast-moving objects with ease and even predict the subsequent movements of those objects. The ability to track and predict movement is largely based on individual skill, as unskilled users have much more trouble tracking fast-moving objects. A fully-evolved Sharingan can track even the quickest opponents, though, like the first ability, it doesn't necessarily mean the user has the ability to react to it. This perception is also 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. It also gives color to chakra. Additionally, the Sharingan grants the user exceptional analytical powers, allowing them to instinctively pick up on various visual clues with little difficulty. For example, Sasuke was able to reproduce answers on another person's test by watching their pencil movements and copying them during the Chunin Exam.

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. It also allows for other forms of hypnotism, such as putting an opponent to sleep, replaying memories to someone else, or creating various illusions to fool an opponent.

It is possible to transplant Sharingan eyes from one person to another, as occurred with Kakashi and his deceased comrade Obito Uchiha. 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. Kakashi keeps it covered when not using it to avoid this side effect in his everyday activities. 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.

Mangekyo Sharingan
The Mangekyo Sharingan (万華鏡写輪眼, Mangekyō Sharingan?, literally "Kaleidoscope Copy Wheel Eye") is a heightened form of Sharingan. It was first awakened by Madara Uchiha, who was able to use it to gain control over the Nine-Tailed Demon Fox. Over the generations other Uchiha came to possess their own Mangekyo Sharingan, though Madara Uchiha, Itachi Uchiha, Kakashi Hatake, and Sasuke Uchiha are the only characters to have possessed it in the current Naruto storyline. Unlike the standard Sharingan, the Mangekyo Sharingan differs between users, changing the form of the Sharingan's tomoe seal when activated. Those who possess a Mangekyo Sharingan suffer from ever-deteriorating eyesight, a process that becomes faster through repeated usage and culminates in blindness. Only by taking the eyes of a sibling can one's eyesight be permanently restored, combining the appearances of the two Mangekyo Sharingan and granting them immense strength in the process.

When the Mangekyo Sharingan is first introduced, Itachi tells Sasuke it can only be gained by killing one's closest friend. Though Itachi and many other Uchiha have done this to obtain their versions, an alternative method is used when Sasuke gains his. After Itachi himself dies as a person with whom Sasuke shared a close relationship, his Mangekyo Sharingan is awakened. Which, if either of these methods, Kakashi used to gain his own remains unknown.