Summoning: Impure World Reincarnation

The Summoning: Impure World Resurrection is a forbidden technique used to revive the dead. It was originally developed by Tobirama Senju, and later completed by Orochimaru. Kabuto now claims to have mastered it to a degree even higher than them. Kabuto also claims this technique to be the "greatest, most powerful technique in the shinobi universe", as it poses no risk at all to the user.

Conditions
To perform this technique, the user must first acquire some of the DNA of the person they intend to revive. 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 revived must also reside in the ; those whose soul has been consumed by the Death God, for example, cannot be resurrected. Next, a living sacrifice is required for the soul of the resurrected 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 revived had at the time of their death. The process is apparently somewhat painful as seen when Fū was used to revive Torune. The person is then revived and the end product is usually stored in a casket until summoned by the user. The user can theoretically revive 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 resurrected 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 asleep. Upon awakening they retain their personality, memories, and all abilities they had in life, including kekkei genkai, kekkei tōta and summoning contracts, but it does not seem to be able to recreate unique weapons such as Samehada (though normal weapons like kunai and shuriken do seem to reform). On the downside, the revived seemed to retain any permanent body damage they received during their lifetime. The summoned all have grey sclera and retain their original eye colours however the entire eye is darkened. When Kabuto takes complete control of them however, they gain black sclera and white irides. . Except for their sclera, the eye colours of dōjutsu wielders don'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 revived individuals to remotely summon coffins containing additional reinforcements.

Control
After the individual has been summoned and awakened, the summoner can bind the individual to his or her 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 resurrected individual will regenerate further, eliminating any remaining imperfections and restoring colour to their bodies and clothing.

Different talismans can be used to enact different degrees of control. Orochimaru'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. Resurrected 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, Kabuto can completely remove their personalities if needed, and may elect to if they resist his command too strongly. After gaining more experience with the technique, and absorbing Orochimaru's chakra from Anko Mitarashi, Kabuto exerts greater control over the summoned and can even overwrite his own talismans, greatly increasing the power of the binding. Once deployed the summoner can either remotely controls or tracks the summoned individuals using pebbles he manipulates on a simple grid, which acts as a map of sorts.

Countering
The revived are impossible to kill by normal means. Any damage they receive will regenerate, be it lost limbs or complete disintegration. Not even killing the summoner will get rid of them. There are three discovered methods to end the technique:
 * 1) Seal away the soul of the revived individual.
 * 2) Have the summoner end the technique. As they are unlikely to do this voluntarily, using a genjutsu to trick them into cancelling the technique is ideal. The sequence of hand seals for cancelling the technique is Dog → Horse → Tiger and saying.
 * 3) The revived individual is affected in some emotional way that gives them closure; Kankurō notes that human emotions are not so easily restrained. However, this method cannot work if the summoner destroys the personality of the revived individual before their soul is freed of its bonds.

Once any of the first three methods are accomplished, the revived bodies will crumble back into dust, leaving the body of the sacrificed individual lying among the ashes.

Aside from the three methods of actually defeating the technique outright, there are three 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 or act. Although this does not truly defeat the summoning, it is effective at neutralising the immediate threat the revived pose in battle. Furthermore, while the resurrected can't be destroyed and feel no pain, they are still vulnerable to things like poison (as shown with Hanzō).
 * 2) If the revived people retain their personalities, they can speak against the user or themselves and give hints and advice to the opponents, as Asuma Sarutobi had done,  even if they are physically fighting against the opponents.
 * 3) A certain powerful genjutsu can free the revived person from the technique's control by giving them an order overwriting the user's control. This possibly means that the summons are as vulnerable to genjutsu as the person was when they are alive.

Trivia

 * In chapter 117 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 chapter 520, Kabuto explains that Orochimaru's attempt to summon the Fourth Hokage had failed due to his soul not residing in the "pure world". In episode 69 of the anime, when Orochimaru used this technique, the coffin briefly appears, with 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.
 * When Kabuto first approached Madara about joining forces, he summoned Deidara, Itachi, Kakuzu, Nagato, and Sasori as a demonstration of power. When Madara threatened to refuse Kabuto's offer, Kabuto summoned a sixth casket that compelled Madara to not only join forces with Kabuto, but to call him a "Madman!". The content of the sixth casket was obstructed from view.
 * The video game, Naruto: Ultimate Ninja 2, the (non-canon) storyline contradicts the idea the soul of the revived must reside in the Pure World, as Orochimaru revives the Third Hokage no differently than anyone else he summons in the game.
 * Kabuto also mentions his desire to resurrect certain shinobi, including:
 * Jiraiya, though his body lies at the bottom of the ocean where the water pressure is too great to reach. However, he claimed that the bloodstains on the Six Paths of Pain's weapons may provide enough DNA.
 * Shisui Uchiha, but Kabuto could not find his body, though he suggested that Shisui's crushed eye, which is in Madara's possession, may be sufficient. Later, after learning that Shisui's other eye was on the battlefield, he seemed excited at the prospect of obtaining it. However, Itachi incinerated it.
 * In the manga, when the First and Second Hokage were resurrected, their eyes appeared blank. But in the anime version, their eyes appeared normal.