I remembered more about that spander I've been looking for, so I'm gonna try again. It's the one where Xan intercepts some kind of magic collar that Angelus sent to Buffy. He puts it on and is turned into a kitten. Whereupon Dru finds him and takes him back to a wheelchair-bound Spike to keep him company. The developing Spander goodness starts when Xan witnesses Angelus beating and furhter abusing Spike, then afterward slips off the collar, becoming human again, and cares for the unconscious vamp.
So, does anyone know it?
please and thank you
Found! Many thanks to debris_k. the fic is Kitten!verse by </a></font>50ftqueenie</b></a></span></font>