This movie is somehow related to Whisper of the heart, it follows Muta (the cat from Whisper of the heart) and Baron (the cat statue in Whisper of the heart, also used in Shizuku's story). The story is based on Neko no Danshaku (Baron of Cat) by Hiiragi Aoi.
The main character of the story is Haru. Haru is a clueless, ordinary 17 year-old girl. She has no special abilities and neither is she an extraordinary beauty. When faced with reality, she is unable to make decisions for herself, thus often swaying to others' opinions to avoid challenge. One day, Haru saved the life of a cat without consideration of her own safety. The cat turned out to be the Cat Prince from the Kingdom of Cats, however as a result, Haru is trapped in the world of cats. Can Baron and Muta rescue Haru who has wandered in the world of cats?