Rinnegan

The is reputed as the most exalted eyes amongst the, along with the Byakugan and the Sharingan. While its progenitor was first seen in Kaguya Ōtsutsuki as the Rinne Sharingan, its true form first manifested in her son, the Sage of the Six Paths. It is characterised by a ripple-like pattern which spreads over the eyeball, with light purple sclerae and irides, and also has another variant containing a pattern of six tomoe.

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. The Rinnegan originated from Kaguya Ōtsutsuki's Rinne Sharingan, and was first truly manifested by her son, Hagoromo Ōtsutsuki, who came to be revered as the Sage of the Six Paths by using his dōjutsu to create the groundwork that brought forth all modern ninjutsu.

For Kaguya to be revived, a person must first awaken the Rinnegan to summon the Demonic Statue of the Outer Path from the moon. To this end, Black Zetsu spent centuries manipulating the reincarnations of Indra and Asura to awaken the Rinnegan by combining their chakra. After centuries of failing, only Madara awakened the Rinnegan through this method.

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, merging the chakra of his two sons, Indra Ōtsutsuki and Asura Ōtsutsuki, within one's body brings forth the Sage's chakra, which can evolve their Sharingan into the Rinnegan. This was proven when Madara Uchiha, Indra's reincarnation at the time, 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 Uchiha awakened a Rinnegan containing six tomoe in his left eye.

Abilities
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 their full power be accessed. Also, only an original owner of this dōjutsu has demonstrated the ability to deactivate the Rinnegan. 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 in his emaciated state and prior to being trained as ashinobi. The Rinnegan also has the ability to negate the blindness of an eye and restore its previous powers upon its awakening. Nagato was never shown to see chakra points unlike Madara, this may be an ability only a original rinnegan owner has along with Amenotejikara and Limbo.

One who possesses the Rinnegan has access to many abilities, such as the ability to possess and use all six chakra 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. The Rinnegan also makes the user immune to visual genjutsu. However as seen with Nagato, the Rinnegan's field of vision can be blocked by simple means such as smoke bombs. It also grants the ability to create chakra receivers for various melee and supplementary purposes. 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. With this dōjutsu, Madara could perform the Limbo: Border Jail technique, creating corporeal shadows which are only visible to the Rinnegan. Sasuke's Rinnegan allows him to shift spaces within a certain range of himself. Sasuke's Rinnegan also retained his Sharingan powers, including his left Mangekyō's technique, Amaterasu, and the ability to cast powerful genjutsu, with which he was able to control all nine tailed beasts at once.

The Rinnegan grants the user multiple abilities which are collectively referred to as the Six Paths Technique. 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 which sport copies of the user's Rinnegan. The Preta Path can absorb chakra in any form. The Naraka Path can make use of the King of Hell for interrogation and restoration.

In addition, the user is granted the Outer Path, which gives them control over life and death. It also allows the user to bind those who touch their chakra 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, and the creatures and reanimated corpses which have copies of the user's Rinnegan.

By embedding up to six corpses with chakra receivers, the user can control the corpses as additional bodies, referred to as the Six Paths of Pain. The corpses possess copies of the user's dōjutsu and each can utilise one of the abilities of the Six Paths Technique, though their usage is inferior to that of the user's main body. Obito made use of this method to control six reincarnated jinchūriki, which had their former tailed beasts temporarily bound to their bodies using chakra receivers while remaining in Obito's possession through the Demonic Statue's chakra chains.

Trivia

 * 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 their names with the six Samsaric realms of reincarnation.
 * The kanji is also used in Sharingan and Rinne Sharingan, potentially linking the three terms etymologically.
 * 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.
 * In the digital manga chapters colourised by Shueisha's production team, Sasuke's Rinnegan was coloured red, like Madara and Kaguya's Rinne Sharingan. Later illustrations coloured by Kishimoto instead depict it with the usual purple colouring. The colouration was corrected in subsequent digitally colourised chapters.