I want to talk about tempering

[LineageRazor]

Note that both Nael and Lousoix had the grip of the primal relinquished off them, The canonicity of that might be questionable but I believe that the effect of tempering can be removed

I think that in Nael's case, at least, it was explicitly stated that Bahamut relinquished his hold on Nael because Nael had died and was no longer of use to him. The "untempered" Nael we witnessed was basically Nael's ghost, just prior to dispersing into the Lifestream. It is certainly possible that tempering ends with an individual's death, in all cases - though if they desire, a sufficiently powerful Primal can choose to hold onto the soul after death and construct a new body for it (again, as was the case with Nael). There's no point in holding onto a disembodied soul with no body, though, so Primals generally don't bother.

I think the primal has to be currently existent to maintain tempering after death, though.

It could be that aether once committed to a primal becomes incompatible with Hydaelyn. In such a case, the aether could very well disperse and exist but still deny Hydaelyn power. If the Ascian-derived summoning methods were part next-level plotting, it may also be the case that such dispersed aether remains compatible with Zodiark, should it (he?) ever need the aether.

I like this theory, and it makes a lot of sense. Primals act as a kind of "converter", changing Hydaelyn-aether into Zodiark-aether. The biggest flaw I see with it, though, is that Ascians seem just as gung-ho on defeating Primals as they are on summoning them. Wouldn't it make more sense for them to promote keeping the Primals around as long as possible to process as much aether as possible before they're destroyed? In ARR, the Ascians were clearly enthusiastic about the WoL defeating Primals, all part of their mysterious plan...

Maybe the act of summoning converts a lot more aether than is converted by the primal just passively existing? In that case, a cycle of repeatedly summoning and destroying a primal would make sense under this theory.

[ObsidianFire]

We've known that Hydaleyn has been in a weakened state ever since the Umbral Eras started. How she got that way... we don't know (yet). I'd argue we've never seen Hydaleyn in her "normal" form. The Primals probably aren't even the chief cause of her losing aether, they're just exacerbating the process and they're something anyone can make.

[Cilia]

Well...

If you'll recall, we needed Matoya's Crystal Eye to try and find Minfilia after she was caught up in Y'shtola's Flow. Unlike in I where it was literally a crystal eye Matoya used to see, this one was an artifact of immense magical power - a Crystal of Light from a bygone era. It's much larger and more powerful than the ones the Warrior of Light possesses, from which it can be surmised that Hydaelyn was indeed more powerful in the past than she is now, and that primals and Calamities are to blame for her weakening.

As to whether aether can be replenished or once it's used up is gone for good? Well... thermodynamics disagrees with the former, but given this is a world of magic that might not apply. There's no conclusive evidence one way or another, but it's best to err on the side of caution.

[Lium]

I always saw tempering as being similar to Mass Effect's indoctrination. Once you're indoctrinated, that's pretty much it. It's irreversible. People who have been indoctrinated, unfortunately, have to be killed. Because it goes way beyond mind control. Indoctrination (and tempering) actually alters your entire being. It's mental, physical, and spiritual. In the ME series, only the Leviathans, the progenitors of the Reapers, can release someone from a Reaper's indoctrination.

It is quite possible, that the Warrior of Light will learn how to reverse tempering in time. We still don't know the extent of the WoL's powers.

[Remedi]

I always saw tempering as being similar to Mass Effect's indoctrination. Once you're indoctrinated, that's pretty much it. It's irreversible. People who have been indoctrinated, unfortunately, have to be killed. Because it goes way beyond mind control. Indoctrination (and tempering) actually alters your entire being. It's mental, physical, and spiritual. In the ME series, only the Leviathans, the progenitors of the Reapers, can release someone from a Reaper's indoctrination.

It is quite possible, that the Warrior of Light will learn how to reverse tempering in time. We still don't know the extent of the WoL's powers.

Note that both Nael and Lousoix had the grip of the primal relinquished off them, The canonicity of that might be questionable but I believe that the effect of tempering can be removed

[Cilia]

It's unknown how exactly Louisoix overcame his tempering. Perhaps because he's also a primal? Anyway, yeah, Bahamut let go of Nael's soul since she wasn't useful anymore. So a primal can voluntarily relinquish their hold on a person, but there must be a way to bring someone to their senses even if that's not the case... unless, again, Louisoix's nature as a fellow primal was what made it possible.

Primals are entropy engines, more or less; their purpose is to distort the flow of aether and create instabilities (not to mention the havoc they wreak on mortal civilizations), bringing the chaos that will return Zodiark. We don't know if the aether primals consume can be replenished, but we do know they have detrimental effects on the landscape around them; the Sagolii desert, for instance, is hinted to be a consequence of Ifrit's summons during the first SMN quest. If the Garlean theory on the Burn being a consequence of repeated summons is true... yeah.

Tempering can produce physical changes, but for the most part it's just warping souls. The only people shown to have biological differences as a result of primal influence are Nael (in her Coil deus Darnus form) and the overdrowned pirates in Sastasha HM.

[Anonymoose]

Just throwing some musing into the pot for consideration of what specifics we have and which are most likely to be at least partially true and relevant.

Minfilia's PowerPoint said that the corporeal form a primal is made of up aether from crystals and the land and such - when a primal dies, that aether goes back into the land to nourish it. If primal aether was lost or forever incompatible, the whole Realm Reborn scenario would have even more explaining to do because the damage caused by the Calamity was mitigated by Phoenix returning its aether to the land - Bahamut just interrupted the process and started eating the aether himself, causing neither the land nor Bahamut to be fully restored.

A primal's soul-like essence is what returns to the Lifestream, presumably to be blended back into aetherial atoms like the soul of whatever responded to the primal beacon to be rematerialized in the first place. Whether that is somehow tainted of incompatible with the Crystal in the sea... not sure, though it'd put a funny twist on the Primalsplosion in the 1.0 cutscene with the detonation of the seal, lol.

[Remedi]

Just throwing some musing into the pot for consideration of what specifics we have and which are most likely to be at least partially true and relevant.

Minfilia's PowerPoint said that the corporeal form a primal is made of up aether from crystals and the land and such - when a primal dies, that aether goes back into the land to nourish it. If primal aether was lost or forever incompatible, the whole Realm Reborn scenario would have even more explaining to do because the damage caused by the Calamity was mitigated by Phoenix returning its aether to the land - Bahamut just interrupted the process and started eating the aether himself, causing neither the land nor Bahamut to be fully restored.

A primal's soul-like essence is what returns to the Lifestream, presumably to be blended back into aetherial atoms like the soul of whatever responded to the primal beacon to be rematerialized in the first place. Whether that is somehow tainted of incompatible with the Crystal in the sea... not sure, though it'd put a funny twist on the Primalsplosion in the 1.0 cutscene with the detonation of the seal, lol.

about the soul-essence, what do we really gather about it? The story is a bit hazy on it, Bahamut , phoenix and Ramuh kinda made me believe that primals had a sense of self, then Hraesvelgr sai that primals were phantoms much like aeons they are created by the imagination of the summoners.
Which kinda makes me wonder what actually hate Ultima and what was the explosion on the seal if that is even still canon

[Cilia]

But... if vanquishing a primal returns its aether to the land, then something like the Burn couldn't come about as a consequence of summons... right?

I mean, the aether used to sustain the primal's corporeal form would naturally have to go somewhere when it's brought down. Back to the land from whence it came would be the natural destination. What about the aether a primal uses for things like tempering, supers, etc.? They have to have some kind of detrimental effect on the world beyond warping the aetherial flow... otherwise they're not that big a deal, and the damage they cause will mend in time. Right?

[Vulcwen]

But... if vanquishing a primal returns its aether to the land, then something like the Burn couldn't come about as a consequence of summons... right?

Well, it could be that the aether moved to other parts of the world. A land drained of aether can't support the lives of a primal's followers, meaning they'd likely have to move to other places, and the primal would move as well.