I don’t like how genasi + aasimar + tieflings are so taxonomical. They could do with being a bit more vague about what high fantasy Paracelsian interpretation they map onto. They could also do to be a but more like Kill Six Billion Demons. 

Aasimar/Fire Genasi

Angels are eternal conflagrations of heatless nuclear flame. They mostly exist in the Void, where they sing endless atomic songs and contemplate their own immanence. Those unfortunate humans descended from angels are aasimar. They are as much flesh as fire, their blood and breath and soul replaced by a single nuclear pneuma that sustains them even as it slowly consumes their bodies.

from kill six billion demons
  • Age: Aasumar live as long as elves. As they age, they become more beautiful, more alien, and more rarefied as their heavenly fire slowly burns away all trace of their temporality. 
  • Alignment: Whatever
  • Speed:  30 ft
  • Languages: English/Common and Enochian/Celestial
  • Ability Score Increases: Your Constitution score increases by 1. Your Wisdom score increases by 2.
  • Rarefied: You are immune to disease and poison and do not breathe. You keep your fire-self burning with sacred oils and blessed incense (function as wine and rations in terms of cost and encumbrance) for fuel. You need to “eat” and “drink” half as much as a human. 
  • Meditation: Though you do not sleep, you must spend 4 hours a day contemplating the Void or find yourself slowly drawn back there in a state that conveniently mirrors human exhaustion. You are fully aware of your surroundings in this state.
  • Radioactive: You can cast the Produce Flame cantrip
  • Body of Fire: You have resistance to radiant damage