Rammstein lyrics! Probably out of everyone's comfort zone but I think that could be a good thing! The lyrics to many songs are metaphorical and I find lend themselves nicely to femslash. Two examples being "he says I stole you / he doesn't know / that you love me" from Roter Sand (Red Sand) and "There is love for everyone – not for me" from Liebe ist für alle da. There are also many songs that explore toxic and/or plain unhealthy relationships, which I think femslash deserves to have explored (or just written in general, I love drama).

I remember someone suggesting mythical creatures a while back so I'd like to propose that myself! You could dig into some more obscure ones as well to make people really think. I'd be very interested to see what people do with something like 'serpopard' or the questing beast!

Weapons would also be a fun prompt because of how flexible you can be with the prompts, since in the modern day even diseases can be classed as weapons. Many weapons have symbolic associations as well, such as daggers with betrayal and swords with honor. also if 'claymore' is a prompt then that's a possible gateway drug to people discovering Claymore the manga but SHHHH nobody must know my agenda. https://en.wikipedia.org/wiki/List_of_premodern_combat_weapons