TheSharingan, literally meaning "Copy Wheel Eye", is a Dōjutsu Kekkei Genkai, which appears in tosome membersof the Uchiha clan. The sharingan holdsseveral stages, each one stronger than the previous one, obtained through continued use and training, up to a maximum of three (tomoes). As the Sharingan evolves, the user gains heightened abilities and a growing mastery over their KG.
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The one tomoe: It allows the user to perceive motions and see chakra.
The two tomoe: At this level the user gains a better understanding of the sharingan. The user can nowanticipate and analyze faster movement, as well as mimic minor movements made by an opponent. The user cannow track higher speeds(almost twice as fast) and, by reading the handseals, can predict to some extent the use of Ninjutsu techniques
The three tomoe: When active the user now has the ability tokeep up with extremely high speedsand mimic basic taijutsu exactly. With this the user cannow copy handseals done by an opponent(using the adequate Copy Technique), and use jutsusas they do
The MS: The link to Genjutsu is further increased and, if the user has gained full mastery over Genjutsu, he gains the ability to castany and every genjutsu without the need for Handseals through simple eye contact. Also, the Mangekyo Sharingan gives the user access topowerful and forbidden techniques, unique to each user
The EMS: the Eternal Mangekyo Sharingan gives the user access to the same powerful and forbidden techniques availabe to the user through his MS and even some additional ones. Uchiha Madara however, has the ability to use not only his unique MS abilities but also the generic ones such as Amaterasu and Tsukiyomi.