Are you sure it was a cat and not a puppy ?? Lol. This one is really close but the ML is a demon that was punished (cursed), he turns into a cute puppy during the day https://www.mangago.zone/read-manga/night_song_mgs/
Could it be ‘Night Song’ that you’re looking for? https://www.mangago.zone/read-manga/night_song_mgs/
OMG YES THIS IS THE ONE!!! I forgot it was a puppy
Yes tyyyyy
I read this bl like 2 years ago and stopped reading till more chapters to release but I never saved it. But it was about I believe the seme who would like have connection with the dead and I think he was cursed or something and would turn into a cat I think during the day and at night visit the uke as a human. The uke was like a emperor or at least someone in a palace and would bump into the seme a lot during the night. There was like a step mother who hated the uke and has tried to get him sick and killed at some point. It gave like painter of the night vibes. I'm like itching to know what happens after cuz I think the uke was about to get kidnapped or something