History of the Uchiha Clan
The Uchiha clan (うちは一族, Uchiha Ichizoku) was one of the four noble clans of Konohagakure, and was also reputed to be the village's most powerful clan, producing shinobi that were exceptionally talented and battle-oriented, and in possession of the renowned Sharingan. The Uchiha clan descended from Indra, the elder of the two sons of the Sage of the Six Paths. Indra inherited the Sage's "eyes", powerful chakra and spiritual energies. When it came time for the Sage to choose a successor, he questioned the two on what course of action they would follow to bring order to the world. Indra believed that power was the way to bring peace, while Asura, the younger son, believed love was the way. The Sage favoured Asura's ideal, and therefore designated him as his successor, causing Indra to be filled with jealousy and hatred. From this hate came what Tobi calls the Curse of Hatred (憎しみの呪い, Nikushimi no Noroi). From Asura descended the Senju clan who would be the eternal rivals of the Uchiha. The Uchiha were famous for their powerful chakra, exceptionally strong techniques, and natural aptitude for anything combat-related. The clan possessed an innate affinity for Fire Release nature transformation, with even the youngest of members able to use it from just observation.
Abilities of the Sharingan
The Sharingan (写輪眼; Literally meaning "Copy Wheel Eye") is a dōjutsu kekkei genkai, which appears in some members of the Uchiha clan. While its powers were first seen in Kaguya Ōtsutsuki, its true form first manifested in Indra, the earliest ancestor of the Uchiha clan, and later became regarded as one of the Three Great Dōjutsu 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. Tobirama Senju defines it as the "eye that reflects the heart" (心を写す瞳, Kokoro o utsusu hitomi).
The Sharingan's abilities consist of two parts: the "Eye of Insight" (Dōsatsugan) and the "Eye of Hypnotism" (Saimingan). The first of the Sharingan's powers is being able to see chakra flow. The Sharingan itself gives color to chakra, allowing the wielder to differentiate them. They are also able to tell if a person is under a genjutsu because the person's chakra flow would be irregular.
The 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. As the Sharingan evolves, gaining more tomoe, this ability extends to being able to track fast-moving objects before finally giving some amount of predictive capabilities to the user, allowing them to see the image of an attacker's next move from the slightest muscle tension in their body and counter-attack or dodge without any wasted movement. However, even though the user may be able to see an attack or know it is coming, their body may not always have time to react.
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 memorize 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, much like Sasuke Uchiha's Lion Combo. In order to reproduce a copied technique, however, one must have the necessary skill or ability to perform them. In addition to physical skill and kekkei genkai techniques, the Sharingan cannot reproduce techniques dependent on other factors, such as summons that the user has not signed a contract with, or KGs that the user does not have.
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. The hypnotic ability coupled with the other aspects of the Sharingan can make the user appear as if they can "see the future". First, the user must perfectly mimic every move their opponent makes and possibly their thoughts and words through careful observation. Then, they suggest an action to the opponent such as hand seals for a technique that the opponent and Sharingan user already know and copy that. With these things done, the user can complete the action even before the opponent does, possibly using the Sharingan's genjutsu to confuse or delay them. As with other genjutsu, genjutsu cast by the Sharingan are capable of putting an opponent to sleep, inducing paralysis, replaying memories to someone else via genjutsu, or creating various illusions to deceive someone or torture the person. The potency of the Sharingan's illusion is dependent on the user's knowledge and skill with implementing genjutsu. Two Sharingan users are also able to free each other from other forms of genjutsu by first using genjutsu on each other, allowing them to enter their comrades mind and free each other from the genjutsu.
Upon reaching the Third Tomoe, the user is capable of awakening his Mangekyo Sharingan, though this is very rare due to the conditions required. The Mangekyō Sharingan is awakened by a Sharingan user when they suffer from trauma after witnessing the death of someone close to them. It 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 with all known wielders of the dōjutsu having eyes that resemble variations of pinwheels.
The Mangekyō Sharingan gives the user's eyes enhanced might to the standard Sharingan's generic abilities and access to powerful techniques. Using the Mangekyō Sharingan puts strain on the user's eyes and erodes their vision, eventually causing blindness. This can be prevented by transplanting another pair of Mangekyō Sharingan from a close relative, such as a sibling. The newly acquired Mangekyō Sharingan looks like a merger of both eyes and is dubbed the Eternal Mangekyō Sharingan (永遠の万華鏡写輪眼, Eien no Mangekyō Sharingan)