1, sona has like this infection/parasite thing. it has a similar fading mark like arlecchinos, just a light-icy blue thats on her hands up to her forearms and legs up to her knees + spotting along her ribs and waist. 2, she has a huge scar along the left side of her waist, i have no lore on that yet. 3, she's quite friendly with a lot of the women in fontaine and often visits chiori and emilie when she goes to the surface. yume-fact, i'll do souwrio dynamic, they very much are cat in dog, in the sense that wrio is affectionately annoying and sou begrudgingly accepts it but also does adore it.
so basically, V!XEN were originally angels but because they couldn't maintain order between all species, they were punished and forced to live the rest of their lives as fallen angels with painful rebirths. they can still use their powers, its just signifigantly weaker in their fallen state (theyre technically still strong, but theres a huge power difference).