This movie started when Studio Ghibli received a proposal from a Japanese theme park to make a twenty-minute animation starring cats.
So far, this is Studio Ghibli's only spin-off or sequel feature film.
This was originally going to be a short straight-to-video project, but producer Toshio Suzuki was so impressed with director Hiroyuki Morita's storyboards, and especially the main character of "Haru", that he encouraged Planner Hayao Miyazaki to give this a cinematic release.
Took three years to complete.
While every other cat in the human world and the Cat Kingdom has paws, the Baron has human-shaped hands, covered in gloves and sporting long fingers and visible thumbs. He is also noticeably smaller in the human world, about two-thirds the size of an average cat. These attributes mirror those seen on the Baron figurine in Whisper of the Heart (1995).