Living Corpse Reincarnation

The Living Corpse Reincarnation is a technique that was developed by Orochimaru that allows him to transfer his soul to someone else's body. It is also referred to as the "Eternal Youth and Immortality Technique". It was developed in order to fuel his dream of acquiring all the knowledge in existence, a feat that cannot be achieved in a single lifetime.

Usage
The Living Corpse Reincarnation immortalises one's mind, transferring it to a stronger body before the current host rots. By repeating this process periodically, this effectively allows the user to remain in the realm of living, so long as they can keep the host body alive while residing within.

Orochimaru can only perform this technique once every three years. It also seems that when the three years are almost over, he is forced to move into another host, as the previous one begins to weaken and reject him. Presumably, if he had a proper container, he could stay in the host for a full lifetime. The fact that he wanted to prepare Sasuke Uchiha and Kimimaro for the transfer before performing it reinforces this.

To perform this technique, Orochimaru reveals his true form: a gigantic white snake composed of smaller white snakes, by abandoning his current host's body. Orochimaru then swallows the new host and takes him or her to a separate, mental plane where he envelops the mind of his victim. The snake body then dies and falls apart, and Orochimaru's soul dominates the body (though the Sharingan seems to be able to negate and reverse the process against Orochimaru). The souls of the hosts are kept alive within Orochimaru, leaving them "still alive", in a sense (albeit suppressed), and when Orochimaru switches hosts, the souls leave with him. Apparently if the host of these souls' chakra level falls enough it is possible for them to resurface in material form as seen with Orochimaru surfacing with his own body after Sasuke used up most of his chakra.

After taking over another body, Orochimaru modifies it to suit his theme of snakes, in order to increase his survival capabilities, such as stretching and bending his body, reconnecting any severed parts, and shedding his skin to heal injuries. This ensures that if Orochimaru cannot transfer body within the three years' time, he can allow it to greatly heal and evade attacks, rendering him virtually immortal; Sasuke refers this as the. Orochimaru also alters the face of his host body to look like his original form.

After being revived through the Evil Releasing Method, Orochimaru seemingly circumvented this process, emerged in a slightly different snake form and simply slithered into a White Zetsu clone's mouth.

Hosts

 * 1) Unknown person — when Orochimaru uses his Living Corpse Reincarnation on Sasuke, one of his past hosts is seen in Orochimaru and Sasuke's mental plane.
 * 2) Unknown female — for replacing the hand Itachi Uchiha severed; left body to escape the effects of his arms being sealed away.
 * 3) Gen'yūmaru — a desperate temporary replacement body before Sasuke Uchiha; left body for Sasuke Uchiha.
 * 4) Sasuke Uchiha — after having been absorbed into Sasuke when he reversed his Living Corpse Reincarnation, took over due to Itachi lowering Sasuke's chakra enough for Orochimaru to gain control; was sealed away by Itachi.
 * 5) White Zetsu Clone — for the cells of Hashirama Senju, as well as to escape the fatal injury of releasing the Dead Demon Consuming Seal.

Candidates

 * Itachi Uchiha — for the Sharingan; failed due to Orochimaru being unable to defeat him.
 * Kimimaro — for the Shikotsumyaku; rejected due to terminal disease.
 * Guren — for the Crystal Release; rejected due to being too late and loss of interest.(anime only)
 * Sasuke Uchiha — for the Sharingan; postponed due to being overpowered, then sealed away before released by the Evil Releasing Method.