Redaku Reincarnation Ninjutsu

This reincarnation ninjutsu is one of the many subjects documented at the centuries-old Astronomy Research Institute, an archive of knowledge for the Land of Redaku. A few years prior to the events of Sasuke Retsuden, Zansūru, an archaeologist, deciphered enough of the relevant research to learn how to use this technique. However, because he was not a ninja, he recruited Gigi to perform it on his behalf. A few decades prior to this, Orochimaru visited the Institute to research this technique, ultimately stealing a few of the more valuable documents for his own purposes and using what he learned to improve upon Tobirama Senju's Impure World Reincarnation.

Overview
This technique is similar to the Impure World Reincarnation in many ways, to the point that Sasuke Uchiha initially believes they are the same. Zansūru insists that the Impure World Reincarnation is merely a regional variant. Like the Impure World Reincarnation, this technique brings back souls of the dead using living sacrifices; Gigi exclusively reincarnates dinosaurs (more commonly called "dragons"), but also planned to reincarnate a human, Margo, until he found out that she wasn't actually dead. Gigi summons a dinosaur's soul using its fossilized remains and places its soul in the body of the live sacrifice: a chicken, one of the closest extant relatives of dinosaurs. Dust and ash encase the chicken's body, giving it the same size and appearance as the dinosaur had in life.

The dinosaur's reincarnated body retains all the physical skills it had when it was alive, with the added advantage of being immortal; it can be damaged, but its body will repair itself indefinitely regardless of severity. Not all wounds heal at the same speed, with burns being observed to still linger after several days. Unlike the humans reincarnated with the Impure World Reincarnation, who don't seem fazed by injuries, the dinosaurs reincarnated with this technique still feel pain. Yet because they can't die, they must suffer through any injuries that would ordinarily kill them until their body is healed. This detail draws empathy from Sasuke, prompting him to avoid injuring the dinosaurs when possible: he believes Amaterasu could be used to "kill" the dinosaurs, burning them until there's no longer any body left to be repaired, but decides not to try it so as not to subject them to the prolonged pain that would cause.

How the user controls the reincarnated is never made clear, only that there are no talismans placed in the skulls as is done with the Impure World Reincarnation. The user's control over those they reincarnate is great enough that it can't be overcome with standard genjutsu. Sasuke is able to somewhat erode the control over one dinosaur, Menō, by speaking to him kindly, refusing to harm him, and by offering to return him to the afterlife, something that Menō wants. This momentarily allows him to establish control over Menō with a genjutsu, which he then makes permanent by channeling his chakra into Menō's body to overwrite Gigi's control.

Having control of a reincarnated form grants certain advantages. Information gathered by the reincarnated can be instantly passed along to their controller, such as to help the controller locate somebody they're searching for. Conversely, the controller can pass some of their chakra to the reincarnated, enhancing their strength: Menō, a juvenile of his species, is able to overpower an adult of the same species because he has access to Sasuke's chakra. Control of one or more reincarnated subjects can be granted to non-users - as Gigi does to Zansūru - but these non-users cannot give commands that are too complicated. Furthermore, new commands will immediately override previous commands regardless of potential consequences; Zansūru at one point commands a flying dinosaur to let him ride it, but later gives the same dinosaur a new command unrelated to being ridden, causing Zansūru to fall off and die upon impact with the ground. If and when the non-user dies, any commands they gave are rescinded and the original user's most recent commands take effect again.

To release this technique, the user performs the same hand seals that are used to initiate it in the first place, thus freeing the souls (even those under the control of another) from their reincarnated bodies. The souls do not immediately return to the afterlife, instead lingering in their bodies for a few moments; this brief delay gives Sasuke and Menō a chance to exchange farewells. One dinosaur is even shown clinging to its reincarnated body, using the brief window of no longer being controlled to attack Gigi, vengeance for having brought it back to the living world. Once the souls do finally depart, their body disintegrates back into the dust and ash that they were made of.

Known reincarnated

 * Tairano - a bipedal carnivore, identified as one of the strongest dinosaurs to be reincarnated. Adults have hind-legs twice the height of a human; Menō, a juvenile of this species, can travel twelve meters in a single spring, making him fast enough that even Sasuke cannot outrun him. This species has a long, powerful tail that it can hit targets with, which can easily be swung at targets from the side if they block its forward attacks. The species' sharps claws and powerful jaws can effortlessly separate flesh from bone. Its name, "Tairano", is presumably a reference to Tyrannosaurus.
 * Pterosaur - flying dinosaurs that are around ten meters tall. They possess incredibly sharp beaks, which can easily pierce deeply through flesh or bone. However, the beaks are not strong enough for actual combat and will start to dull after delivering only a few blows to a target(s). Weighing less than ten kilograms, they are very light, allowing them to fly to destinations quickly. This lightness works against them if captured by an opponent, as even a small number of attacks will prove debilitating to them.
 * Kabinaga, nicknamed "Titan" - a long-necked dinosaur reaching thirty meters in length, it is one of the largest creatures in history. Because of its sheer size, any building it walks into will be extensively damaged and anything it steps on will be pulverized. Its size is a handicap in many ways, preventing it from changing directions quickly and rendering it unable to reach any enemies attacking its back. Its great weight makes walking across certain terrains precarious, and if any of its comparatively short legs is injured, it likely will not be able to support itself, causing it to fall over. Its nickname, "Titan", is presumably a reference to the Titanosaurs.
 * A human-sized dinosaur that is highly flexible. Its relatively small size makes it easy to bite targets, at which point it runs off, leaving its targets to bleed to death. It is described as resembling a Spinosaurus.
 * A herbivore with a thick dome-shaped skull that is likened to iron. It lowers its head and charges at targets, trampling those that get underfoot and launching those its skull collides with high into the air, killing them on impact. It is shown cornering targets in confined spaces and slamming its feet on the ground as intimidation before launching its attack. Its description matches Pachycephalosaurus.
 * A bird-like dinosaur that searches for targets through scent. Once it finds a target, it runs to their location, swaying as it moves. If the target tries to hide, it can use its talons to dig through obstacles. A herbivore, only the legs of this species can reasonably be used for attacks, and even then it requires multiples of its species attacking at once if it wants to defeat an opponent. Its description is similar to Archaeopteryx.