yaoi that involved cats? uke turns into cat when he gets scared and the seme finds the cat...

Sounds like the story related to the kuroneko series but with the calico.

http://www.mangago.zone/read-manga/nekoka_kareshi_no_ayashikata/

Did you ever find out which one this was? I know exactly what you’re talking about but I can’t remember it either beyond one part where the uke in cat form goes, “tummy snuggles!?”