It seems that the Thaumaturges might really borrow their powers from the "remnants" of Bard's eidolon each time they pray to it in combat.
Also what if that shadow was part of the Radiant itself? It could be funny to see it being completely pitch black unlike its name
Hmmm... interesting possibility.
Funnily enough... despite the name of the manga, despite the fact nemesis are the "enemies" of humankind... for quite some time we haven't focused on them really.
They are always there, their presence IS always felt, all the conflicts stem from nemesis presence... but compared to the cruelties done by people, they feel more like... nature.
Even Seth's quest to find the radiant feels something out of mind most of the time, especially after Cyfandir.
Now... the shadow being connected to the nemesis... part of me feels like that makes sense... but another feels like it doesn't.
The shadow is connected to Piodon, which is connected to the whole thing that goes with Seth's family, and now we know it is old, maybe primordial even. By the looks of it, nemesis weren't present during this era... can't even remember if they mentioned when they started to appear.
In my mind... since we got more details about fantasia during the Cyfandir arc, and about the existence of the Sidh... i kinda see nemesis like... not like true enemies of humanity, but a method for nature itself to regulate the flow of fantasia.
What they are, how they interact with fantasia, why they seem made of fantasia, why survivors of touching them get those "infections"... all of these are questions that come to mind.
And a theory comes to mind about the "infections"... when someone resistant touches a nemesis, what shocks them may not be fantasia per se... but that they are connecting to the different layers of the Sidh, to the many possibilities of their own lives, but their bodies and minds cant grasp the information or energy flowing completely... so they get... "remade", and the "infection" is a side effect of a incomplete and brusk remake, like a "bug" into the very existence.