Masashi Kishimoto's hugely popular manga Naruto is a staple in the manga and anime community, as well as a former member of Shonen Jump's 'Big Three' alongside One Piece and Bleach. One of the most exciting aspects of the battle manga is its unique power system (Ninjutsu), which allows for many unique abilities, such as the fan-favorite kekkai-genkei the Sharingan, used by many different characters.
Introduced early on in the series, the Sharingan is an ability passed down through generations of the Uchiha clan. As the series progressed, the Sharingan began to acquire more and more capabilities, making it one of the more overdeveloped powers in Naruto. As such, not only does it have a laundry list of extraordinary powers and awakenings, but it has a long history as well, making some of its lesser-known aspects easy to forget.
The Sharingan Requires Special Circumstances to Awaken
While the Sharingan may be passed down through the Uchiha genetically, it does not mean that every Uchiha will awaken the ability. For an Uchiha to awaken the base form of the Sharingan, the individual must endure a powerful emotional experience, releasing a unique form of chakra in the Uchiha's brain. This particular chakra then transforms their eyes, via the optic nerve, into the Sharingan. This can be seen in the series when Sasuke awakens his Sharingan for the first time after witnessing his brother Itachi slaughter their entire clan, including their parents.
Because of this unique awakening trait, the Sharingan has become referred to as the Uchiha's 'Curse of Hatred.' This is because members of the Uchiha clan tend to love more deeply than others but become consumed by hatred when they awaken their Sharingan via emotional trauma.
The 'Original' Sharingan Has Three Forms
Many fans of Naruto are familiar with the next stage of the Sharingan, known as the Mangekyo Sharingan. In exchange for killing one's best friend, the Sharingan wielder is granted immense power in the form of an evolved Sharingan. However, many fans may have forgotten that the original or base form, Sharingan, also evolves over time.
After awakening their Sharingan, Uchihas typically possess one tomoe in their eye. This is a visual representation of the eye's immaturity. As a result, immature eyes will not be as proficient in wielding the Sharingan's abilities. However, through emotional stress and experience, the eyes will mature until they each have three tomoe, signaling the full maturation of the kekkei-genkai.
The Sharingan Can Be Split into Two Abilities
The literal translation for the Sharingan is "Copy Wheel Eye." When the Sharingan was first revealed in Naruto, its abilities were far less over-powered than they were by the story's end. Kishimoto, who is well known for his ability to retcon, likely did not know quite how far he would develop the Sharingan's abilities at the beginning of the series. Instead, he probably intended for the exact opposite, as the original abilities of the ocular jutsu were far more subtle than its Mangekyo counterpart.
The original Sharingan can be divided into two separate abilities: 'The Eye of Insight' and 'The Eye of Hypnotism.' The Eye of Insight essentially allows the Sharingan user to see chakra and perceive visual input at a minute level. Kakashi Hatake used this ability so much he was given the nickname, 'Copy Ninja,' due to his tendency to utilize the Sharingan to copy his opponent's jutsu. During the "Chunin Exam" arc, Sasuke also utilized this ability to perfectly copy the movements of another genin during the written test, allowing him to cheat successfully.
The Eye of Hypnotism, however, as the name suggests, is based on genjutsu. This ability allows users to trap their opponents within a genjutsu much more easily than the average shinobi in order to more easily escape from an opponent's genjutsu.
Not All Users of the Mangekyo Sharingan Have the Same Abilities
While the method of obtaining the Mangekyo Sharingan is consistent (intense emotional trauma), the abilities it grants each user can differ. Typically, each eye will possess a different power, but there is a third ability that requires both eyes.
The first user of the Mangekyo Sharingan introduced in Naruto is Itachi Uchiha. Within each of his eyes, Itachi is said to possess both the ultimate genjutsu in his Tsukuyomi and the ultimate physical attack in his Amaterasu. In conjunction with both of these abilities, Itachi also had the Susanoo, which required both of his eyes to activate.
Much like his brother, Sasuke possessed both the Amaterasu and Susanoo after awakening the Mangekyo Sharingan; however, instead of developing the Tsukuyomi like his brother, Sasuke developed the ability to control the shape of the Amaterasu in his other eye. Interestingly, Sasuke did not develop the Tsukuyomi even after transplanting Itachi's eyes into himself, indicating that the ability is based on the user and not the eye itself.
Unlike the pair of brothers, Obito Uchiha developed Kamui in his eyes after awakening the Mangekyo Sharingan. Because one of his eyes was possessed by Kakashi, he was unable to use the Susanoo. However, when Obito granted Kakashi the use of both of his eyes, he was able to activate it during his fight against Kaguya.
The Sharingan Evolves into the Rinnegan
Another popular ocular kekkei-genkai is the Rinnegan. First used in Naruto by Nagato, otherwise known as Pain, the ability is rumored to have been descended from the Sage of Six Paths himself. As you'd expect from this, it displayed great power, with six unique jutsu. However, before the Fourth Great Ninja War, there was no indication that this was an ability developed from the Sharingan, particularly since Nagato had been revealed to be an Uzumaki clan descendant.
However, two pieces of evidence prove the Sharingan matures into the Rinnegan. The first can be seen in the reanimated Madara's fight against the Shinobi alliance. After being attacked by Naruto, Madara is forced to activate his Rinnegan as his Mangekyo Sharingan could not absorb Naruto's jutsu. Following the revelation that he possessed the Rinnegan, Madara revealed that he acquired the ability after implanting the First Hokage's cells into his body. As this mixed the chakras of the Senju and Uchiha -- resulting in the chakra of the Sage of Six Path's chakra -- the Rinnegan appeared. Madara also stated that it was his Rinnegan that was implanted into Nagato, revealing how a non-Uchiha could obtain the ability.
The second instance of the Sharingan evolving into the Rinnegan can be seen after Sasuke receives a portion of the Sage of Six Path's Chakra. Afterward, Sasuke's left eye evolves from the Mangekyo Sharingan to the Rinnegan, granting him all its abilities.
