Puraneko: Planet of the Cats

Near future. The people has colonized the Space. The protag is an average doctor, he travels around the numerous planets on his own starship. He and his cat Nery is the only "crew" up there. Because of onboard AI system malfunction, the ship crashes and lands on a strange planet populated with nekomimi humanoid race, and his lovely pet suddenly transforms into one of the same kind...

[from WinKi-tyan]