Fanfiction-buffy the vampire slayer:if i think that you might like me by SummerFrost

Summary:
"Giles got turned into a cat?" Riley asks. "That guy can't catch a break."
"Oh, no, common misconception," says Spike. "Rupert and human Rupert are different people."

Or: Spike adopts a very dumb orange cat who helps him experience the power of friendship and, more importantly, psychologically torment Giles.