Uchiha

The Uchiha clan (うちは一族, Uchiha Ichizoku) was one of the clans in the Land Of Fire, and was also reputed to be the most powerful clan, producing shinobi that were exceptionally talented and battle-oriented, and in possession of the renowned Sharingan. Their current leader is Yusai Uchiha.

The Sharingan When an Uchiha experiences a powerful emotional condition with regards to a person precious to them, their brain releases a special form of chakra that affects the optic nerves, transforming the eyes into Sharingan; for that reason the Sharingan is described as an "eye that reflects the heart" (心を写す瞳, Kokoro o utsusu hitomi). Often, as per the Uchiha's so-called "Curse of Hatred", this emotion is a negative one, brought on by stress or loss. The emotion can also be positive, driven by a desire to protect or reunite with a loved one.Assuming that the user is aware they have awakened the Sharingan,[4] they are thereafter able to freely use it. When first awakened each Sharingan usually will have only one tomoe (巴), although in Obito Uchiha's case, he immediately gained two tomoe in each of his eyes. Through training and continued use the Sharingan will develop a second tomoe and then, upon full maturation, a third. All the Sharingan's abilities are available to the user from its earliest stage, but with greater development comes greater proficiency with those abilities. As with any dōjutsu, Sharingan can be transplanted into non-Uchiha. They are unable to deactivate it and its use has a greater chakra demand for them than for actual Uchiha, who need only minimal chakra to keep it active. For these reasons, non-Uchiha tend to cover their Sharingan when they aren't using it in order to conserve chakra. Sharingan that originate from the same Uchiha are still linked to some extent even when wielded by separate users, at times enabling those users to see the same things.