Sharingan is a dōjutsu of the Uchiha clan, manifesting selectively in 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 grows emotionally, it reaches three, achieving full maturity; all abilities are available from the first stage, merely strengthening 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 reading lips, tracking fast-moving objects, and predicting an opponent's actions by the slightest muscle movements. This enables reading hand seals and copying virtually any observed technique — whether ninjutsu, genjutsu, or taijutsu — reproducing them or adapting them to oneself. The "Eye of Hypnosis" through eye contact implants thoughts and actions into the target's mind, 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's pattern appears in the victim's eye. With this power, the Uchiha became famous for suppressing 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 blurs 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 of 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, thus 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.
