As part of the bits and bobs I'm writing for Nanowrimo this year, I wrote a bit about Illya getting a kitten, in celebration of me getting yet another cat (she's called Ariana, she's a year old, she's very sweet). It's Gen, as Gen as the series is, at any rate, which means it's as slashy as you want it to be, and kind of fluffy.
Link goes to AO3.