Soul/Tensei Chūkaku

Tensei Chūkaku (転生 中核; lit. "Incarnation Core"), otherwise known as a spiritual imprint, is the accumulation of a spirit's life times. It contains the knowledge that remains, even when a spirit is reincarnated.

Overview
Tensei Chūkaku (転生 中核; lit. "Incarnation Core") is an extremely elusive aspect of the soul that is heard only in legends. The scholarly community have yet to confirm or rule out it's existence - albeit, there are still a bevy of rumors that suggest the average soul has actually been in existence for at least two decades, with 'new' souls being a relatively fresh occurrence.

The Tensei Chūkaku can be seen as a permanent records of sorts, as it contains the total accumulation of all a soul's worldly experiences. Rarely is this aspect of a person's essence ever tapped into - but in the rare cases it is, this is usually a person's past consciousness aiming to provide insight or knowledge. In rarer cases, a person may be spiritually in-tune with this part of the soul, and thus can readily communicate with their past selves as a form of guidance or tutelage.

Despite the spiritual imprint containing all the information of past lives, there are certain cases where a person's former identity may still exist in other dimensions, or realms. This, however, normally is a byproduct of the techniques that often defy or pervert the natural order of things.

Certain individuals may also obtain such powerful souls that they may be able to produce tenshō (転生; lit. "transmigrant") otherwise known as transmigrants. In these exceptional cases, rather than passing on freely into the spiritual realm, particularly powerful entities may travel along and find a new vessel. It's there that their energy fuses into the person - normally a child or newborn, as the youth's spirits are still in development in that stage - implanting all of their knowledge and information within the soul's spiritual imprint.

In these rare cases, at certain trigger points, the vessel of this transmigrant may be capable of utilizing the powerful chakra and abilities of their last life - a feat that would otherwise be impossible.Normally, however, to be able to use the full extent of a previous life's might, the person's body must be compatible, such as with the ability to use kekkei genkai.