Aasimar

Aasimar
Aasimar can follow one of two realisations of the race. The first maintains the 5e sourcebooks concept of them, being plane touched beings who have been born with connection to an extraplanar celestial called a 'deva'. The second is more of a mutation like that of a Tiefling.

Feel free to play either kind.

Angelic reincarnation:
When mortals die, their souls traverse to the Astral Plane until they come across the Underscape where they are judged for the life they lived, and either sent to the Eternal Citadel, the Seven Hells or the Herebetween.

Eventually however, all souls are reincarnated in the Prime Material when another mortal is born. When a soul has spent such a duration in its afterlife that is consciousness starts to fade, they are sent to be reincarnated. Additionally when a celestial or fiend is killed, their soul is reincarnated instantly.

When a soul reincarnates, it tends to be a fresh start. However, extraplanar influence is hard to separate from a soul if it becomes too entwined. Hence why very rarely, an angels soul can reincarnate into an Aasimar, and a Fiends soul can reincarnate into a Tiefling.

Sent to the Prime Material:
The other kind of Aasimar is the more traditional 5e sourcebook kind.

When a soul is sent to the Eternal Citadel after being judged in the Underscape, it goes through a second judgment when it arrives. Some souls that have done good, did it for the wrong reasons for instance. If a soul has made it to the Eternal Citadel, but is then turned away at the door - it is given a second chance.

The soul is sent back to earth to be reincarnated as an Aasimar with connections to a Deva. An angelic being in the Eternal Citadel who provides a constant vigil over the Aasimar. They decide over the course of their life if the soul is to be welcomed into the Eternal Citadel, or be cast to the Herebetween.

Unlike the 5e sourcebooks, the Aasimar are not sent with a specific purpose in mind. They are sent to be reincarnated, with the potential of a guaranteed entrance to the Eternal Citadel if they live a good life. The Deva however, chooses how to interact with this Aasimar, and if they want to give it missions, so be it.