Outer Path — Samsara of Heavenly Life Technique

The Outer Path — Samsara of Heavenly Life Technique is a reincarnation ninjutsu used through the Outer Path, which can infuse new life into the bodies of those who have died in exchange for the user's own life.

Usage
To perform this technique, the user summons the King of Hell, which then releases the souls of the deceased from its mouth. With their rejuvenated bodies acting as an anchor, the deceased individuals' souls are able to leave even the crossroad between life and the afterlife, returning back to their physical vessels. While using this technique, the user is severely weakened and their hair becomes white, a result of overexerting their power. Ultimately, once the technique is finished, the user inevitably dies.

This technique can also be used on those brought back to life by Summoning: Impure World Reincarnation, transforming the debris and ash that forms their corpse vessel into a real body of living flesh and blood, even if they have been dead for many years. However, there appear to be limitations to this usage, as while the rest of Madara Uchiha's body was made real, his eyes instead crumbled into dust upon his resurrection.

The exact range and power of this technique are unknown, but on separate occasions it has targeted a large number of recently deceased individuals and a single individual who has been dead for more than a decade.

Influences
As with many of the Rinnegan's techniques, it is influenced by Buddhist terminology. , derived from the Sanskrit Tīrthika, refers to any doctrine which "treads the outer path" to enlightenment. This is opposed to the teachings of orthodox Buddhism, the, and is thus considered misguided and heretical.

Trivia

 * When written as '輪廻転生', Rinne Tensei means "the circle of transmigration" or "metempsychosis".
 * When Nagato was preparing to use this technique, Konan feared for the worst due to him being low on chakra, implying he could have potentially survived its usage. However, the fourth databook clarified that usage of this technique comes at the cost of the user's life.
 * Madara — and Obito under the guise of Madara — noted that this technique was supposed to be used to revive him. Madara would eventually be reincarnated anyway, and expressed surprise and disappointment that his return didn't go as planned, as only a living person can become the Ten-Tails' jinchūriki. Eventually, Black Zetsu successfully forced Obito to perform this technique on Madara.
 * Despite using this technique, Obito was able to live a little longer thanks to Black Zetsu attaching to him, and subsequently because of Naruto Uzumaki's Yin–Yang Release, though both of them knew that Obito would ultimately die because of the technique's side effect.