Its already the name of a Minmatar Fighter in Eve. Nice try but I also don't think the Amarr would resort to naming things after minimar conventions (minnies have vikings)

I believe the name applied would depend on the culture - amarr use Templar and would probably use nephilim, the gallente would be the likely users of elysians (a lot of the names they use come from Greek myth), the minmatar would likely use einherjiar... As for the caldari I propose the word "Rasetsu" - a type of demon or unrighteous spirit that subsists mostly off of violence and has a lot of connotations towards being an eater of human flesh or a drinker of blood and as par for most spirit creatures in Asian myth is notoriously hard to kill and supremely skilled with weapons being more or less an incarnation of violence.

Collectively all would fall under the word 'immortal'

I think that whatever your uninterrupted consciousness is connected to and can control is considered your body. The original body thing doesn't even make any sense once you realize that every molecule in your body is replaced within 11 years. Not a single molecule that was 'you' 11 years ago is still part of you. You are your consciousness.

Mercenary is fine.