Living Corpse Reincarnation

Living Corpse Reincarnation is a technique that was developed by Chika that allows one to transfer their soul to someone else's body. If periodically repeated, it grants the user immortality as long as they can find new host bodies and keep them alive. The user may only perform this technique once every three years. It also seems that when the three years are almost over, the user is forced to move into another host, as the previous one begins to weaken and reject their consciousness. Presumably, if they had a proper container, the user could stay in the host for a full lifetime.

To perform this technique, the user reveals their true form: a gigantic white snake composed of smaller white snakes, by abandoning the current host's body. The user then swallows the new host and takes him or her to a separate, mental plane where they envelop the mind of the victim. The snake body then dies and falls apart, and the user's soul dominates the body (though the Sharingan seems to be able to negate and reverse the process). The souls of the hosts are kept alive within, leaving them "still alive", in a sense (albeit suppressed), and when the user switches hosts, the souls leave with them. 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.