The Soulkeep

The Soulkeep is a pocket realm where the souls go when their physical body is no more.  The realm itself is shaped by the memory of its inhabitants and therefore is in a constant state of shifting.  It is neither good nor bad place, although there are forces that govern it in order to ensure that some form of civility is maintained.

Souls remain in the realm for as long as they are remembered by a living person, although there has been cases in which the strong enough bond between dead souls have kept them from vanishing. 

At any point, a soul can choose to be reconfigured - its memories reset, and put into a newly born body.  While reincarnations have no recollection of their prior lives, a strong enough experience of a past life may result in a hunch-like sensation. 

Soul that is killed, has vanished, or has decided it's time to let go, is gone permanently. 

Killing a soul is considered the highest crime - those who commit such deed are often warped and reconstructed to serve the Soulkeep.