An aasimar is a humanoid creature born on the Material Plane who possesses a spark from a divine plane, often the realm of a Havilonian deity. An aasimar is always born for a specific purpose, a goal of their deity, and they each have a divine guide with whom they can commune. Aasimar are incredibly rare and appear with glowing eyes and other luminous features that reveal their heritage.
They appear in humanoid lineages, but whichever family an aasimar originates from, they nonetheless possess only the traits of an aasimar and appear to look more like which deity has blessed them. An aasimar born in an orcish family but blessed by Veil might look distinctly elvish instead of orcish.
Some of these divine chosen champions stray from their path, either by choice or due to some corruption; these are called defected aasimar. The defected aasimar do not necessarily have a divine guide, and often forge their own path — often one of destruction.
Aasimar are not infertile, though their children are whatever race the other parent is. This sometimes makes them very attractive to people who wish to keep their bloodline pure.
Aasimar have the potential to become ageless if they fulfill the purpose they were created for, and said creator grants them this level of immortality. Usually, an aasimar also has a guaranteed spot in their deity's divine domain unless they really messed up badly in life.
Their souls are immortal, and one who does mess up badly, and has lived an evil life too far from the path laid before them, are reincarnated upon death as a rakshasa. Likewise, with rakshasa, they may become reincarnated as aasimar. Upon reincarnation, they do not retain their memories of past selves unless granted access to them by a higher being.