I'm on mobile so I can't see the FAQ so idk if you guys will answer this but if I made a fuschia blood fantroll(in an AU of course)would her lusus have to be Feferis?Or is it possible for it to be different? I want to stick close to canon

There are only two fuchsia bloods in existence at a time, the Condesce and the heiress. So if you’re writing about one of the heiresses before Feferi then go for it. Also there’s a link to the FAQ in the description which you can see on mobile.