All of them!
Well no, some are really absurd to say the least. As there’s just so many I think I’ll stick with Yuyuko x Mystia for this post.
Yuyuko: Hang on. Got a bone in my throat…
Youmu: Didn’t you just say you didn’t like sparrows?
Yuyuko: It’s not good to be a picky eater, Youmu.
It was jokingly implyed in Imperishable Night that Yuyuko ate Mystia after defeating her, although the fact she’s seen later on in Phantasmagoria of Flower View. Nowhere does it suggest any form of relationship became of that.