This is a super half-baked theory because I still want to actually go back and bring in a bunch of textual evidence but I’m too lazy to do that right now, so you’ll just have to trust me.
Chiori’s story quest was one big allegory the whole time — Chiori represents Phanes, her ex-partner Luther (most likely named after Luther Pendragon) represents Nibelung, and “fashion” represents “fate.” Following this story, Phanes and Nibelung were once partners who had a falling out because Nibelung started using “bad materials” to craft fate — I could see this being the actual cause of the Khaenri’ahn curse, somehow.
In the quest about the fall of Remuria, we find out that Remus and Scylla actually worked together in secret, even though they were supposed to be fighting each other. Remus (Phanes) made a deal with Scylla (Nibelung) to have him attack the capital while Remus slept, leading to the destruction of the kingdom. After that, Scylla was sealed away under the capital, and Remus woke up to see Remuria sink underwater.
Lastly, I’m just going to point you to my other theory that Itto & Paimon represent Nibelung & Phanes. There’s something weird going on with those two, and their little rivalry-turned-friendship seems to be a big part of the story lately.