Now, Aster was sure that he could quench a part of his curiosity, by using his dragon eyes to scan Agnes's soul avatar, contrary to what most people believe, even ethereal beings have a "solid" thing to them.
The explanation is actually quite simple, ethereal beings manifest in energy form, so they are bound to have meridians, just like cultivators, anything that wishes to circulate energy has meridians, they just have a different name or form depending on the nature of its owner.
For example, the "meridians" of a formation are the runes used to create it, veins, organs or bones can be meridians for body cultivators, if we take a page from Aster's previous world, the cables of an electronic would be meridians, that's the best way to see it, anything which can circulate energy has the potential to be a meridian.