Because he is not a member of the Uchiha clan, Kakashi's Sharingan is always active and he expends chakra rapidly when using it, forcing him to withdraw in combat or sacrifice his life energy and needing extended rest after long battles. Kakashi Hatake possessed a single, transplanted Sharingan in his left eye that he received from his teammate, Obito Uchiha. It is possible for the user to have a different number of tomoe in each eye. When first acquired, the Sharingan may have one or two tomoe, acquiring more tomoe until it fully matures, having three tomoe in each eye. After awakening the Sharingan, the user may use it freely. Because of the psychological effects it can have in obtaining it and evolving it, many have referred to the Sharingan as the 'Curse of Hatred', including the Second Hokage. It is not immediately present from birth, and first activates when the user experiences a strong sensation of despair that causes a special chakra to be released from the brain and alter the user's eyes.
The Sharingan first manifests in Kaguya's grandson, Indra, who became the founding ancestor of the Uchiha Clan.
The is a genetic attribute within the Uchiha Clan that is descended from Rinne Sharingan, an ancient dojutsu possessed by Kaguya Otsutsuki the Sharingan retains its red iris and sclera as well as three of its tomoe.
