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 Jiji 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; Jiji 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. Jiji summons a dinosaur's soul using its fossilised 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. In the novel, it also has 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 with undying flames and rendering them incapacitated, but decides not to try it so as not to subject them to the prolonged pain that would cause. However in the anime adaptation this jutsu lacks most of the immortality advantages. The reincarnated beings bleed and can be killed with a serious enough damage.
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 channelling his chakra into Menō's body to overwrite Jiji'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 Jiji 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 Jiji, 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.
