Power source for Heritage Found and Everkeep

[Andoriel]

Where is the aether coming from for the Barrier and Everkeep? Is it being drawn from Yak Tural or are they in some way still connected to the 9th?

[Cleretic]

It's not entirely clear (nor likely that important), so we're down to personal speculation. And my best guess is basically 'they brought it with them'. Alexandria's dome is clearly much bigger and operates somewhat differently than Treno's, so I do think it's entirely possible that, intentionally or not, they dragged the Ninth's own ecosystem with hem.

[NegativeS]

Considering a portion of Everkeep is still poking out into their home plane, it doesn't seem too out of the ordinary that they're just draining Lightning from there.

There's a lot to go around.

[Cleretic]

Considering a portion of Everkeep is still poking out into their home plane, it doesn't seem too out of the ordinary that they're just draining Lightning from there.

Is there? Living Memory isn't part of the Everkeep, it was just organizationally disguised as 'the twelfth floor' while actually being above the dome. And I'm not sure what other part you might be thinking of.

[Dikatis]

Where is the aether coming from for the Barrier and Everkeep? Is it being drawn from Yak Tural or are they in some way still connected to the 9th?

Well, Everkeep is powered by lightning because virtually all of its infrastructure is made of electrope. It's constantly being struck by lightning and you can see lightning rods littered throughout Heritage Found erected for the explicit purpose of drawing power from the countless lightning strikes that go off every day.

As for the dome itself, it's never fully explained, but it's reasonable to posit that when Alexandria merged itself with Yyasulani, it brought some of the conditions of the Ninth with it. The wibbly-wobbly Rejoining-adjacent nature of interdimensional fusion probably permanently changed weather patterns and created that dome out of some kind of weird spacial/reality-bending phenomenon.