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The Sharingan is a dōjutsu kekkei genkai of the Uchiha clan, appearing selectively among its members and revered as one of the Three Great Dōjutsu alongside the Byakugan and Rinnegan. Its awakening is triggered by a strong emotional experience directed at a loved one — the brain releases special chakra that affects the optic nerves and transforms the eyes into the Sharingan, which is why it is called "the eye that reflects the heart." Initially, the eye bears one tomoe, but as the bearer matures emotionally, it develops up to three, reaching full maturity; all abilities are available from the first stage, simply growing stronger with development.

The Sharingan possesses two fundamental properties. The "Eye of Insight" allows one to see chakra, distinguishing its colors, sources, and composition, recognize illusions and clones, notice anomalies in others' chakra flow, and even view chakra through certain obstacles. Perception sharpens to the point of lip reading, tracking fast-moving objects, and predicting an opponent's actions by the slightest muscle movement. This makes it possible to read hand seals and copy virtually any observed technique — whether ninjutsu, genjutsu, or taijutsu — reproducing them or adapting them to one's own style. The "Eye of Hypnosis" uses eye contact to implant thoughts and actions into a target, forcing them to reveal information or act in a certain way, often without the victim's awareness. Under full control, the body is directly subjugated, and the Sharingan pattern appears in the victim's eye. With this power, the Uchiha became famous for their ability to suppress tailed beasts by penetrating the jinchūriki's subconscious and controlling the beast's chakra. The skillful combination of movement copying and suggestion creates the illusion of foreseeing the future.

Additionally, the Sharingan grants access to two forbidden techniques: Izanagi briefly erases the boundary between reality and illusion, turning death into a delusion and rewriting reality, while Izanami traps the target in an endless loop independent of the five senses, serving as punishment for those who abuse Izanagi. The cost for each is irreversible blindness in the used eye.

The Sharingan can be transplanted into someone who is not an Uchiha, but such a bearer cannot deactivate the eye and expends noticeably more chakra to maintain it, usually covering it with something. Further evolution leads to the Mangekyō Sharingan through the trauma of losing a loved one, and the mixing of Ashura's and Indra's chakra can transform the Sharingan into the Rinnegan.