Summoning: Impure World Reincarnation (Ten Tails)

The Summoning: Impure World Reincarnation is a forbidden technique where, using a living person as a vessel, a deceased person's soul can be called back to the world of the living and bound to it. The vessel will then take on the form that person had in life, thereby reincarnating them to do their summoner's bidding.

Overview
It was originally developed by. Madara Uchiha claimed it to be intended for the dead to be reincarnated into soldiers able to clear a battlefield with devastating and otherwise suicidal attacks. The technique was learned by who modified it for his ends. Orochimaru's aide,, claiming that this technique to be the greatest and most powerful technique in the shinobi universe due to it posing no risk at all to the user, mastered it to a greater degree than the previous users. To perform this technique, the user must first acquire some of the of the person they intend to reincarnate. Kabuto remarks that this basically amounts to grave-robbing, although blood stains or organs salvaged after the target's death also work. The soul of the intended reincarnated must also reside in the (浄土, jōdo); for example, those whose soul has been consumed by the Death God cannot be reincarnated. However, if it is a case where the souls are freed from inside the Shinigami, then a user of this technique is free to reincarnate them once again. Next, a living sacrifice is required for the soul of the reincarnated to use as a vessel. Once all prerequisites for the technique have been met, the acquired DNA of the person is smeared on a special scroll and once the scroll is activated, the remains spread out in the form of a special seal with the living sacrifice in the centre. Then dust and ash encase the sacrifice's body, giving them the same appearance that the reincarnated had at the time of their death. The process is apparently somewhat painful as seen when was used to reincarnate. The person is then reincarnated and the end product is usually stored in a casket until summoned by the user. The user can theoretically reincarnate a limitless number of people in this way, so long as they have enough sacrifices, chakra and DNA to perform the technique.

Summoning
When first summoned, the body of the reincarnated is stored in a coffin; their body will appear grey and in a state of minor "decay": marred by cracks and other imperfections, and the individual will also appear to be "disengaged". Upon awakening they retain their personality, memories, and all abilities they had in life, including, and summoning contracts. Although clothing is also retained by the reincarnated shinobi, weaponry on the other items are not and must be procured by the user when necessary, as seen when two members of the were unable to retrieve their weapons from a scroll upon reincarnation, as they were currently in the possession of others. However, once obtained, shinobi that have stored their weapons in or about their person are still able to re-summon their tools, regardless of the number of times they are stored within their respective coffin. As a downside, the reincarnated seem to retain any permanent body damage and physical limitations they received during their lifetime. The summoned all have grey sclerae and retain their original eye colors, however, the entire eye is darkened. When the user of the technique takes complete control of them, however, they gain black sclerae and white irides. The appearance of a reincarnated dōjutsu wielder's eye doesn't change at all. The summoned can be recalled at will by the user, causing an empty coffin to emerge and reclaim the individual, and the summoner can also use reincarnated individuals to remotely summon coffins containing additional reinforcements.

Control
After the individual has been summoned and awakened, the summoner can bind the individual to their will by using a special talisman, which is attached to the end of a kunai and implanted in the brain. Upon implanting the talisman, the reincarnated individual will regenerate further, eliminating any remaining imperfections with the exception of small cracks that may run across the body and restoring colour to their bodies.

Different talismans can be used to enact different degrees of control. Orochimaru and Raian's talismans completely eliminated the personalities of the summoned, turning them into mindless killing machines under his command. Kabuto prefers to use a weaker binding talisman on certain individuals, allowing them to retain some degree of their own personality. The latter method is useful for psychological warfare, and can also allow the summoned individual to tap into their own emotions, memories, or creativity to enhance their effectiveness in combat, but also carries a host of drawbacks; it takes more effort to retain control with the weaker binding which can make it possible for the hearts of the summoned to be swayed by strong emotions, which can result in the soul breaking free and returning to the Pure World, or the reincarnated contradicting orders that they are given. Reincarnated shinobi with their personalities still intact have their movements limited to certain actions, and are basically on "auto-pilot" to react to enemy techniques. Once they recognise an enemy technique their bodies are programmed to counter it with an appropriate method. Even so, the user can always completely remove their personalities if he needed, and may elect to if they resist his or her command too strongly. Once deployed, he can either remotely control or track the summoned individuals using pebbles he manipulates on a simple grid, which acts as a map of sorts. When a reincarnated person is sealed, the pebble cracks and disappears, and the reincarnated shinobi can no longer be used to summon others. This was seen when Haku and Zabuza were immobilised by Kakashi, Maki, and the rest of their division. The pebble for his trump card was black in colour while the others are light-colored. The summoner can also directly talk through the summoned individual.

Provided the summoner has not eliminated the reincarnated person's personality, they can break the link binding him or her to the summoner, as Madara Uchiha did. In doing so, they take full control of their being and if the technique is cancelled, they will remain under their own power, with the immortal body and chakra the technique provides.

Enhancement
Unlike while they were still alive, the reincarnated have unlimited chakra, as well as seemingly near-unlimited stamina and can fight continuously, as neither Kimimaro nor Itachi showed any fatigue from their illnesses as they did in life, and Itachi was even able to use multiple Mangekyō Sharingan techniques without showing exhaustion, while minor uses caused fatigue in life.

The reincarnated are impossible to kill by normal means. Any damage they receive will easily regenerate, be it lost limbs or complete disintegration. Not even killing the summoner will get rid of them. The summoned can make practical use of the this regeneration ability by using suicide attacks and large scale ninjutsu to wipe out everything on a battlefield and then simply regenerate.

The user can also modify their summoned fighters, as he did with Madara Uchiha. While the technique usually reincarnates the deceased at the exact state they were in at the time of their deaths, Kabuto noted that he brought Madara back in a state that was "beyond his prime" and was reincarnated much younger than when he died an old man as well as instilling him with abilities he had acquired in his old age.

and Raian Uchiha can also modify the eyes of the reincarnated shinobi to match his own, as well as resealing the tailed beasts back into their respective hosts.

Countering
While the reincarnated are immune to traditional attacks such as weapon-based attacks and even the death of the summoner being ineffective, there are three discovered methods to end the technique:
 * 1) Seal away the soul of the reincarnated individual with a sealing technique.
 * 2) Have the summoner end the technique. As they are unlikely to do this voluntarily, using a  to trick them into cancelling the technique is ideal. The sequence of hand seals for cancelling the technique is Rat → Ox → Monkey → Tiger → Dragon → Boar and saying "release" (解, kai) (when demonstrating the technique to Obito, Kabuto lied that the seals to release it are Dog → Horse → Tiger). If the summoner dies before the technique is deactivated, then this method is impossible.
 * 3) The reincarnated individual is affected in some emotional way that gives them closure;  notes that human emotions are not so easily restrained. However, this method cannot work if the summoner eradicates the personality of the reincarnated individual before their soul is freed of its bonds.

Once any of the first three methods are accomplished, the reincarnated individual will briefly regain their personalities before crumbling back into dust, leaving the bodies of the sacrificed individuals lying among the ashes. If the technique is cancelled by the user, the reincarnated's bodies are surrounded by a light before beginning to deconstruct. After this, the reincarnated individual's soul will begin to ascend, leaving behind the corpse of their vessel.

Aside from the three methods of actually defeating the technique outright, there are four discovered methods of countering the effectiveness of this technique:
 * 1) The technique can be partially combated by immobilising the bodies in a way that it cannot move, act, or be recalled by the summoner. Although this does not truly defeat the summoning, it is effective at neutralising the immediate threat the reincarnated pose in battle.
 * 2) If the reincarnated still retain their personalities, they can speak against the user or themselves by providing hints and advice to the opponents, even in the midst of involuntarily fighting them. With considerable strength of will, the summoner's authority can even be completely overridden, albeit briefly.
 * 3) A  can free the reincarnated person from the technique's control by giving them an order which overrides the summoner's control. This can be remedied if the user can place a new talisman into the said reincarnated person, thus re-establishing control.
 * 4) What Madara describes as "the one risk of the technique", if the reincarnated knows the specific seal, one can release the Impure World Reincarnation's summoning contract, severing the bond between themselves and the summoner. This leaves the individual effectively immortal with an unlimited amount of chakra, and the summoner has no control over the individual's mind and movements any longer, nor can the technique be deactivated on the said individual.

It should be noted that the reincarnated are still vulnerable to any technique that could affect them while they were alive, but they are able to reform as soon as they receive any damage. Furthermore, while the reincarnated can't be destroyed and feel no pain which originates from bodily harm or mutilation, they are still vulnerable to the drawbacks from their own techniques or weaknesses. Such examples include 's acting as a paralysis agent,  along with the  being left weakened after using certain techniques, and Itachi's eye bleeding on the activation of his Mangekyō Sharingan.

Trivia

 * "Edo" (穢土, Dirty Soil) is what Japanese Buddhists call the normal world, unenlightened people live in. The current, living world. The world of the people who have not yet have escaped the polluting thoughts (greed, hatred, delusion, etc.) that result in suffering.
 * A possible translation of Tensei is "Resurrection". In terms of this technique, both "Reincarnation" and "Resurrection" can be found; the sacrificed body is reincarnated into the body of the summoned shinobi, while the reincarnated shinobi is resurrected from the dead.
 * In of the manga, when Orochimaru first performs the technique, he tries to summon a third coffin. When the coffin is not summoned, he comments on its failure. Years later, in, Kabuto explains that Orochimaru's attempt to summon the  had failed due to his soul not residing in the "Pure World", which Orochimaru was not aware of. In  of the anime, when Orochimaru used this technique, the coffin briefly appears, with "four" (四, Yon) written on it; though the summoning of the Fourth Hokage still fails. Based on Kabuto's demonstration, it would seem the actual failure would have occurred when Orochimaru performed the original preparatory ritual.
 * It would appear that the user's own soul needs to be whole before attempting this technique. Despite being able to use his arms before and after being, Orochimaru was unable to perform this technique until he his own arms from the Dead Demon Consuming Seal.