The Rinnegan (輪廻眼; Literally meaning "Samsāra Eye") is considered the most powerful of the "Three Great Dōjutsu" (三大瞳術, San Daidōjutsu; Literally meaning "Three Great Eye Techniques") and is the third and final evolution of the Sharingan dōjutsu line.
Like the Mangekyō Sharingan, the Rinnegan has been known to take on several unique patterns, though the most common is a ripple-like pattern which spreads across the entire eyeball, along with light purple sclera and irides. Other variations include a purple ripple pattern with tomoe used by Ryun Uchiha, white ripple pattern with tomoe used by Sigma, red ripple with tomoe used by Sasuke and Hiruka, and blue ripple with tomoe used by Phizo Uchiha.
The Rinnegan first surfaced in the Shinju as a single eye atop the tree deity's massive flower. During a time of great strife in the land, Princess Kaguya Ōtsutsuki ate of the fruit of the Shinju, gaining chakra for herself and awakening a third eye which became known as the Sharingan. Under unknown circumstances, however, her eye underwent an evolution and became a Rinnegan in the exact likeness of the Shinju's own single eye. Through her Rinnegan, Kaguya cast the Infinite Tsukuyomi on the entire world.
Sometime later, Kaguya gave birth to a son, Hagoromo—later known the world over as the Sage of the Six Paths—who also managed to awaken the Rinnegan. Through his use of the Rinnegan, Hagoromo was said to have created Ninshū, which later became the modern art of ninjutsu. As a result of the Sage's mythical status, many people believed the Rinnegan was only a legend or a mutation. Because the Rinnegan was wielded by the Sage of the Six Paths, re-merging the chakra of his two sons, Indra and Asura, in one's body can lead to that person awakening this dōjutsu.
This was proven when Madara Uchiha, Indra's transmigrant at the time, later awakened the dōjutsu from his Eternal Mangekyō Sharingan by infusing the DNA of Hashirama Senju, Asura's transmigrant at the time, into his body; however, it did not manifest until many years later when he was near death. At some point after this, Madara would implant his eyes into Nagato—a young boy of Senju lineage. Under the guise of Madara and inheriting the former's work, Obito Uchiha claimed that he was entitled to take the Rinnegan from Nagato's body after his death. He then implanted the left Rinnegan into himself and hid the right Rinnegan, unable to handle the power of both eyes. Madara later managed to retrieve his own left Rinnegan from Obito and, by approaching the moon, awakened the third Rinnegan in his forehead, allowing him to cast the Infinite Tsukuyomi.
After receiving half of Hagoromo's power, Sasuke's left eye transformed into a red-coloured Rinnegan with a tomoe pattern, similar to that of the Shinju and Kaguya.
Like his predecessor, Ryun was an exponentially powerful Uchiha shinobi who was capable of awakening the Mangekyō Sharingan and obtaining its "eternal" counterpart. After meeting an aging Madara in his youth, Ryun managed to gain access to Hashirama's DNA, which contained the power of Asura's chakra. Later, during a climatic battle with Seireitou Hyūga, Ryun subconsciously met with Hagoromo and learned to harness the unique chakra being born within himself, allowing him to awaken his own Rinnegan.
One who gains the Rinnegan has access to a multitude of abilities, such as the potential to master all five basic nature transformations, and the capacity to use any technique. The Rinnegan allows the user to see chakra, including the chakra points within the body, as well as otherwise invisible barriers. However, the Rinnegan's field of vision can be blocked by simple means such as smoke bombs. This dōjutsu can also completely decipher the Sage of the Six Paths' tablet, unlike the Sharingan and Mangekyō Sharingan.
The Rinnegan grants the ability to summon and control the Demonic Statue of the Outer Path, though this cannot be done using an inauthentic Rinnegan. This dōjutsu can be used to perform the a variety of "Limbo" (輪墓, Rinbo) techniques, which involve creating corporal shadows which can only be seen by the Rinnegan. The red-coloured Rinnegan possessed by the Shinju and its jinchūriki is able to cast the Infinite Tsukuyomi, a powerful genjutsu which can only be countered by another Rinnegan user.
One of the Rinnegan's trademark techniques is the Six Paths Technique, which grants the user multiple abilities. The Deva Path can be used to attract and repel targets. The Asura Path can clad the user in mechanized armor and grant them various weapons. The Human Path can read minds, at the cost of ripping out the victim's soul. The Animal Path can summon various creatures. The Preta Path can absorb any chakra-based ninjutsu. The Naraka Path can summon the King of Hell, which can be used for interrogation and restoration.
The various abilities of Rinnegan remain intact upon being transplanted into another individual, but only when both eyes are wielded by the original owner can the full power of the Rinnegan be accessed. Also, only Madara and Ryun, who were both an original owner of this dōjutsu, have demonstrated the ability to change their Rinnegan into into its Mangekyō Sharingan form and back at will. Rather than deactivating his Rinnegan, however, Sasuke is instead seen shutting his left eye when not using it.
Receiving the Rinnegan
Like the Sharingan, the Rinnegan can be transplanted. However, because of its power and immensely strong chakra, not all individuals are capable of handling a transplanted Rinnegan, a trait which is worsened by attempting to implant two. Despite this, the Rinnegan does not appear to have a noticeable effect on one's chakra reserves, as Nagato wielded it for years unhindered, even prior to being trained as a shinobi.
Obtaining the Third Eye
According to Madara, should anyone, wielding the power of the Rinnegan, move closer to the moon, a third eye will emerge, bringing forth from it a Rinnegan that is identical to that of Kaguya and the Shinju's. While this third eye can act as a normal eye, and as a third Rinnegan, its primary function is to allow the user to cast the Infinite Tsukuyomi genjutsu upon the surface of the moon.
This Rinnegan is unique, in that it is red and possesses nine tomoe, causing it to bear a striking resemblance to the Sharingan. Ryun Uchiha refers to this eye as the "third Rinnegan" (三番輪廻眼, Sanban Rinnegan; Literally meaning "Third Saṃsāra Eye"). According to Hagoromo, this eye contains the "power of the Sharingan" (写輪眼の力, Sharingan no chikara), allowing it to perform Sharingan techniques which Rinnegan cannot usually perform.