Transmigration

refers to the process where the chakra of a deceased human remains after said human's death before attaching itself to a new host. The host of this transmigrated chakra is referred to as a.

Process
The Sage of the Six Paths, Hagoromo Ōtsutsuki, seems to suggest that only powerful chakras—such as his sons, and —can remain behind after the deaths of their hosts.

Upon the death of the host, this powerful chakra remains behind, waiting for a specific individual to be born. Once this individual is, in fact, born, the chakra will latch on to the newborn and become part of the newborn's power. In addition to inheriting the chakra of the deceased person, the new transmigrant can also inherit other traits. In the case of Hagoromo and his youngest son, Asura, their transmigrants went on to inherit their powerful wills and desires. In the case of Hagoromo's oldest son, Indra, his transmigrants were capable of both awakening the Susanoo (as well as fully maturing it), as well as inheriting his curse.

Once a transmigrant dies, the chakra of the original once more detaches and manifests itself into another newborn, thus repeating the cycle.