I am currently creating an Aasimar Paladin, and for better protection from EVIL, I figured a paladin would like to have Deathless Spirit over his Celestial Resistances. However, these are "Racial traits," so I figured there would be a way to physically or emotionally express a "Deathless Spirit."
They are traits after all, and a trait kinda makes up who you are. However, I am coming to somewhat of a blank what a "Deathless Spirit" would be.
The only hint I have is that the Racial Trait does say "strong-willed" as a part of its description. This makes me think of the whole DETERMINATION thing from Undertale or how a character from an anime called Goblin Slayer just refuses to let fate kill him.
What is your advice on Role Playing a paladin with a Deathless Spirit for their racial trait? Was I on the right path or do you have better/interesting examples?
I think your assessment of the strong willed character is about right. They simply refuse to allow their will to be bent by the forces of negative energy, even as their bodies begin to suffer from its effects. To some degree, their will alters the fabric of the universe slightly enough around them to provide some minor protections.
As for role playing someone with that kind of willpower, I'd suggest someone with a deterministic outlook, thinking that wanting something badly enough opens up roads to achieving their desires. In the case of a Paladin, that could extend towards believing that everyone has the capability to achieve perfection (or something close to it) and those that don't have chosen not to follow that path, willingly or through ignorance, and it is your duty to enlighten them. That can be as good or bad as you choose to make it, whether a personality quirk or flaw.