I want to talk about tempering

[ObsidianFire]

To further complicate matters... It's highly likely that a Primal should only be considered "normal" when they aren't summoned. Their default state of existence (where they aren't putting a strain on anything as far as we know) is as some kind of beings in the Aetherial Sea. Only unlike living things that die, go back to the Aetherial Sea as aether and then are reborn as something else, they never naturally leave it. I don't know if it's quite fair to say that primals can't exist without consuming aether as the bulk of their existence happens someplace that is nothing but aether. And the Ascians certainly don't want them staying there as that doesn't further their goals (as far as we know). I think it's more accurate that the primals can only survive in an aether-rich environment and the material realm simply has far, far, far less aether then they need.
As a result, they've got two options, go back to the Aetherial Sea or absorb what aether the material realm has. However, them going back to the Aetherial Sea doesn't help the Ascians (that we've seen). It probably isn't a coincidence that the first summonings we see are of gods that are always supposed to be around in myths. So "leaving" isn't something they are going to want to do. Others of them seem to have goals that they want to accomplish, but it would take too long for them to complete them (or their goals can't be realized for obvious reasons). And then there are some primals that actually do accomplish their goals/purposes. Alexander is supposed to find the best future, it just so happens to be one where he's not around. Susano wants to see which of you are the stronger, which happens. Rahmu needs you to kill him if he judges that you're worthy of the job. I'd be interested to see what would happen if a primal's goal was fulfilled that didn't automatically lead to them being forced out of the material realm and back to the Aetherial Sea.

Headcanon Part

Personally, the most fascinating part of this is how different the primals are in myths vs how they are now. Ifrit was someone who rewarded the strength of the Amaja'a's ancestors, not someone killed of their enemies for example. Titan fills O'Guarmo with ore so the Kobolds can defend themselves. Leviathan brought water to a desert area and died from it. Bismark creates the sky islands instead of destroying them (this difference is mentioned in-game). Given that it was apparently possible to summon primals before Silvertear Skies... there's no reason any of the primals we fight now weren't summoned before. I'm kinda wondering if the "original" Primals in the Aetherial Sea are more like the mythic versions of the primals and are getting more then a bit frustrated because of all the constant summonings. And getting really annoyed that their supposed followers aren't at least giving them the goals/desires they're supposed to have.

Ironically... most of the beasts in the Beast Tribes quests end up doing things that are a lot closer to what the mythic versions of the primals do...

[Cilia]

The important thing to remember there is that primals... aren't natural beings. They are the beliefs and wishes of mortals made physically manifest; they exist only due to mortal desire, so unless summoned in the first place they don't exist at all. This is what makes the only theoretical way to permanently kill a primal wiping out all traces of its memory - as long as someone remembers a primal (or myths surrounding it) it should still exist in the aetherial plane. Their entropic nature and immaterial existence is precisely what makes stopping the primal threat for good nigh-impossible.

It's lightly implied that primals are twisted into something advantageous to the Ascians' goals - at least when it comes to summons carried out using the Ascian-taught ritual, which most are. Primals summoned by Echo users who Incarnate Summon are naturally exempt from this, but so too is Louisoix, who became Phoenix due to the fervent prayers of Eorzeans and the massive amount of aether drawn for re-sealing Bahamut.

[LineageRazor]

One thing that I'm curious about, is whether Aether drained by Primals regenerates over time, or if it's gone forever. Aether seems to be tied to Hyaedalyn in an intimate way; she is weakened when Aether is abused, which is very likely why Ascians are so gung-ho on Primal summoning. Presuming that the summonings were to stop, though, would Hyaedalyn eventually recover, and return Aether to the world (including Aether-drained areas like the Burn), or is her current diminished state a permanent thing?

If Aether can be restored over time, perhaps the existence of a single Primal would not be that big a deal. That could be the rationale behind Ifrit's and Garuda's insistence on other summons being heretical - as long as they're the only one on the block, Hydaelyn can handle the strain, and they get to promote their agenda without worry of long-term harm coming to the planet via Aether drain.

The existence of the Burn might imply that lost Aether is a permanent change - but, on the other hand, the Burn was a pretty extreme case, and may simply take a long time to heal - time the Ascians are not allowing her, with their continued harassment.

[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

[Eisenhower]

One thing that I'm curious about, is whether Aether drained by Primals regenerates over time, or if it's gone forever.

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.

[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.

[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.