Replaying Fire Emblem: Three Houses for the upcoming FE "Crimson Flower"

I've been playing the Crimson Flower route of Fire Emblem: Three Houses since last month. I've already cleared Silver Snow, Verdant Wind, and the DLC. There's still a lot I don't understand about Duscur... Apparently, gods are a familiar presence in Duscur, but how does Sothis tie into that? It's not the Church of Seiros, but is there a Sothis faith? I heard the 'Chains of Dromi' were a thing in Duscur.