Theory of relating this film to 'Whisper of the Heart'
"The Cat Returns" has been considered to be a sequel to "Whisper of the Heart." Even so, this is not entirely accurate.
One reason for this, is that 'Whisper' takes place in a very normal world, whereas in 'Cat Returns,' Haru meets cats that walk upright, and journeys to their kingdom, as well as turning into a cat.
I was watching the film with a friend today, and I came up with a very plausible theory for 'The Cat Returns' existence. The theory is, that this is a story written by Shizuku from 'Whisper of the Heart.' Take the following examples:
The Baron- He is originally a statue named Baron Humbert Von Gikkingen. Shizuku in 'Whisper' was told this information by the man who owned the statue of the Baron.
Muta (aka in the cat world, Renaldo Moon)- Muta is known by several aliases. The same can be said of the cat that Shizuku follows in 'Whisper.' A large cat that seems to just wander wherever he pleases. That cat is also known by different names. Seiji (the boy Shizuku meets) calls him Moon ('Because he looks like a full moon,' jokes Seiji). Seiji says that he's heard other households and people calling the large cat different names, one example being Ball. Later on, Shizuku sees the large cat leaving a nearby house, and a little girl calling after the cat, calling him Muta.
These clues leave me to one plausible theory-that the story was written sometime after the events in 'Whisper of the Heart,' probably sometime after she and Seiji married. Given that she's privy to the Baron's original name given to him by his artisan, as well as the different variations of the large cat's names.
There is also a tie-in of a theme used in 'Whisper of the Heart.'
A-ha-ha-ha, you're really weird!-Willy Wonka