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

[Jandor]

Where do you get the "human sacrifice" bit from? They certainly love to offer people's souls to Ifrit and increase the number of worshippers, but no mention I can recall of physical sacrifice, and there are a number of living tempered people around Zanr'ak – there's a whole encampment of tempered Flames who don't seem to be prisoners.

IIRC the original three primals extreme fights have a human sacrifice component to them.

[Iscah]

IIRC the original three primals extreme fights have a human sacrifice component to them.

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.

[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.