
Prerequisite: Protector Aasimar
You have got such a good relationship with your otherworldly guardian that you can transform into it if its willingly.
* Once each long rest you can roll a d20, if you get 5 or more, you transform, gaining glowing blue eyes and to incorporeal, luminous wings to sprout out from your back. You get a flying speed of 40 feet. And you shed bright light in a 60 foot radius and dim light 30 feet beyond that. This lasts for 2 minutes or until you end it as a bonus action on each of your turns.
* Your glow inspires any teammate that can see you, making them immune against frightening and giving them a boost to attack and health. Any teammate that can see you gain bonus health equal to 2x their level and a +2 to any attack or damage roll.
* Thanks to the gift brought upon you, your darkvision is improved, you can now see in darkness as if it were bright light and you can discern color in darkness. This is a passive ability, and isn't affected by your Angelic Appearance ability.
This feat does not interfere with your Radiant Soul ability, but you can't use them at the same time because your soul has switched with your guardian's. If your guardian's soul is somehow detached from its body, you are instantly transformed back into your original form, and you don't have a guardian anymore, making you unable to use this ability again, unless you get another guardian.

Epic
Uhh, some stuff. It's 'Frightened Condition' and you shouldn't need to roll to activate it. It also should be an action much like the radiant soul ability of the original Aasimar. Also the hp gain is called Temporary HP and lastly, pluses to attack rolls and damage is extremely rare and generally, should be advantage. (There are exceptions here and there obviously, but it is a better benefit anyway)
Also Aasimars have Darkvision anyway, aand celestials can't see colour in 5e. So extending it to like 120 feet should be more appropriate. Also this ability should just be an upgrade to the Radiant soul ability, honestly.