Maybe us old timers need to scour side quests and flavor text.

[kaynide]

It's a sacrifice, but willing self-sacrifice of a devoted worshipper – a beastman, not human – to create the ritual foci that fuel the summonings.

I believe the trigger/summoner is that, but the actual primal can consume the aether of others. I want to say that was the deal with Ifrit- he would temper and/or consume people’s aether. Especially those tempered seem to willingly sacrifice themselves for their respective primal.

[Beddict]

From Patch 3.4, Unlikely Allies:

Ga Bu: Th-The...
The patriarch, he...he's...
<gulp> ...The patriarch is going to summon the Great Father again, and you have to stop him! Beat him, fight him, stop him!

Ga Bu: Ga Bu's parents said they didn't want it, along with many others! But the patriarch wouldn't listen. He was so angry─raging, fuming, angry!

Ga Bu: He said that if they didn't have iron in their hearts, they would serve as coke for the furnace. And then the guards took my parents and the others away, and I haven't seen any of them since...

Alphinaud: "Coke for the furnace“?

Alisaie: I did not want to believe it...but I have heard tales of foci fashioned from the bones of beastmen, which worshipers use in their rituals, hoping to summon more powerful incarnations of their gods.

So, Beast Tribes can do ritual sacrifices, and use the bones as foci to summon stronger Primals, but it definitely doesn't have to be from someone willing. Ga Bu's parents totally weren't on board with the summoning despite believing in the Great Father Titan, but they still got axed. While Alisaie does specify that the bones of the beastmen are being used, I wouldn't be surprised if a bone from any sacrificed race works, and it's simply the belief in the power of blood sacrifice that is leading to a stronger summoning.

[KylePearlsand]

....did we ever get around to untempering that loon gah's mother?

All things considered, she's probably far too gone by now. It's mentioned in the 5.55 MSQ that if a tempered is exposed for an extensive and repeated amount of time, there isn't any hope for them. This is seen with the Garleans at Carteneau. She's likely been exposed to Ifrit repeatedly based on her state of mind when she was found.

[GoldStarz]

All things considered, she's probably far too gone by now. It's mentioned in the 5.55 MSQ that if a tempered is exposed for an extensive and repeated amount of time, there isn't any hope for them. This is seen with the Garleans at Carteneau. She's likely been exposed to Ifrit repeatedly based on her state of mind when she was found.

I don't believe this is based on time tempered, since there's no way those Garleans were tempered for longer than a month or so max while Ga Bu was tempered by Titan for several times long as that. I'm pretty sure it's more to do with the repeatedly tempered part and given how Loon Gah's mother doesn't seem to have any lizard-like traits, it's not impossible she could be untempered based off of that.