Just drew all 49 possible combinations. So, no, haven't written anything, just drew up the concept art.
So, no, not technically. I just have ideas for an au.
I'm currently working on my Project Sekai au. But, one day, I'll do like lore stuff for my HSR au, but not a whole fanfiction. I don't have the energy to balance my Genshin verse and my others.
You picked a good thing to reference though.