TobiObito4ever

Well, they arn't actually 'souls' anyway, they are kinda more like ripples on water when something touches it if that makes any sense. A spirit is not really part of the physical world at all, they aren't really anywhere. But in order to interact with the world, they have to sort of force themselves to be somewhere. Wisps and ghosts and other apparitions show up when they do that. Your example sounds like ball lightning, which is very much wisp-like isn't it?

Ball lightning is concentrated, negative-fission plasma supercharged by aetherial energy.

It only occurs with auto-generated electricity. That power plant that had a recursive energy loop blow out and turn the night sky bluish white not too far away from you and very recently likely had small and short-lived close-proximity ball lightning associated with it. Ball lightning has more the appearance of static electricity scaled up a lot than anything and is not always visible to the unaided eye.

The aether is everywhere. Whether it has any visibly rendered parts depends on a multitude of factors, but the 'physical world' wouldn't exist without the aether since everything comes from it and returns to it.

Same with the youkai in the image; they only exist because the aether does and are likely always there, just choosing to not subject themselves to UV exposure.

That's not what the Michelson–Morley experiment tells us, but I think you are talking about something else anyway. Anyway some might say everything comes from and returns to the physical world too. I myself tend to think that any coming or going on the part of everything is probobly purely a matter of perspective.