
While Ifrit speculates that this means the Warrior "already belongs to another" (namely, Hydaelyn,) in fact this immunity comes from a traveler's warding spell, common during Ancient times but unheard of in modern day, that protects a person's aether from corruption.

It's shown that primals can even temper other primals that are tied to mortal hosts by tempering the host when they are vulnerable, such as when Phoenix was enthralled by Bahamut via Bahamut tempering Phoenix's host of Louisoix.This alone makes a Primal exceedingly dangerous even without being a Physical God, and is why The Immune is a hot commodity among the Grand Companies. Brainwashing: They can do this to mortals through a process called tempering (each primal has a different term, though - at least in English - Ifrit's term is typically used as the generic one, since he was the first primal Eorzeans had to deal with), which binds the mortals to their will, making them fanatically loyal until somehow released from their service, usually by death ( or being dismissed by the Primal INTO death).Bonus Boss: Most Primals can be fought again in optional Extreme Trials or Savage Raids, which are much harder than the original battles with them.Baleful Polymorph: The most extreme forms of tempering result in this, with the victims being subjected to so much of the primal's aether that they turn into monsters.Even better, because they were summoned via Loporitts creation magic instead of Ascian summoning they all appear in their truest forms as their worshipers believe.

Back for the Finale: All of the primals worshipped by beast tribes that you've met in your journey are summoned to power the Ragnarok in the climax of Endwalker.
