Rinnegan

The is reputed as the most exalted eyes amongst the. It is characterised by a ripple-like pattern which spreads over the eyeballs, with either light purple sclerae and irides, or red sclerae and irides with a tomoe pattern.

Background
It is said that in times when the world is in disorder, a person is sent down from the heavens to become either a "God of Creation", who will calm the world, or a "Destroyer", who will reduce everything to nothingness. This dōjutsu was first manifested by the Shinju and Kaguya Ōtsutsuki, who ate the Shinju's fruit. Her son, Hagoromo, came to be revered as the Sage of the Six Paths by using his own Rinnegan to create the groundwork that brought forth all modern 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 originally 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 reincarnation at the time, later awakened the dōjutsu from his Eternal Mangekyō Sharingan by infusing the DNA of Hashirama Senju, Asura's reincarnation 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.

When Madara was reincarnated by Kabuto Yakushi to fight the Allied Shinobi Forces, Madara once again gained access to this dōjutsu. Based on data collected over the years, Orochimaru and Kabuto theorised that because the Sharingan originated from the Rinnegan, it was possible for the dōjutsu to change into the Rinnegan as part of a "natural evolution". However, upon Madara's true revival as a living being, he no longer possessed his eyes, as his reincarnated state had been merely a reflection of his former self and he had died without his actual eyes. A White Zetsu managed to retrieve the right Rinnegan from Obito's hiding place and returned it to Madara, who implanted it in his previously empty right eye socket.

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. 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. As a result of Black Zetsu's actions, Madara's body then served as a vessel for the resurrected Kaguya, who retained the Rinnegan in her third eye.

Abilities
One who possesses 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 Limbo: Border Jail technique, creating corporeal shadows which can only be seen by the Rinnegan. The Rinnegan also possesses a unique ability to teleport the user or targets within a certain range of him. The Shinju's Rinnegan, which can manifest as a third eye on its jinchūriki, is able to cast the Infinite Tsukuyomi, a powerful genjutsu which can only be countered by another Rinnegan.

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 mechanised armour 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.

Also, the user is granted the Outer Path, which gives them control over life and death. It also allows the user to transmit their chakra to black receivers as well as manifest the chakra chains of the Demonic Statue, which can be used to bind and control tailed beasts in a similar fashion to the Sharingan and Wood Release. The Outer Path grants a shared field of vision between the Rinnegan wielder, the King of Hell, the creatures summoned through the Animal Path and reanimated corpses, which all have the user's Rinnegan reflected in their respective eyes. By embedding up to six corpses with chakra receivers, the user can control the corpses as extensions of themselves, referred to as the Six Paths of Pain. Each of the corpses is able to utilise one of the abilities of the Six Paths Technique, though their usage is inferior to the user's own body. Obito made use of this method to control six reincarnated jinchūriki. Their eyes sported the Sharingan and Rinnegan, in identical fashion to Obito, and their former tailed beasts were temporarily bound to their bodies using chakra receivers while remaining in Obito's possession through the Demonic Statue.

The various abilities of the 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, who was an original owner of this dōjutsu, has demonstrated the ability to change his eyes from its Rinnegan form into its Mangekyō Sharingan form and back at will. Rather than deactivating his Rinnegan, Sasuke is instead seen shutting his left eye when not using it. Because of its ocular power and potent chakra, not all individuals are capable of handling a transplanted Rinnegan, a trait which is worsened by attempting to implant two. It is unknown what effect this dōjutsu has on one's chakra reserves, though Nagato wielded two transplanted Rinnegan for years unhindered, even prior to being trained as a shinobi.

It appears that Sasuke is still able to retain his usage of Mangekyo Sharingan techniques after he is seen casting black flames upon Kaguya Ōtsutsuki with his Rinnegan in his left eye.

Trivia

 * In the anime, the Rinnegan was depicted as being multicoloured in its first few appearances. Once coloured manga illustrations of the Rinnegan were released, this was corrected. However, whereas the Rinnegan is depicted as a single shade of purple in the manga, the centre-most ring is depicted as a darker purple in the anime.
 * In Naruto: Shippūden episode 203, a silhouette of the Sage of the Six Paths is shown. Here, the Sage's Rinnegan is shown to be red instead of the usual colour.
 * is the Japanese term for Samsara, the cycle of reincarnation or rebirth in several Indian religions. This is reflected in the names of all Six Paths of Pain, which share the names with Samsaric realms of reincarnation.