neko_no_ongaeshi
A Studio Ghibli movie about a girl who accidentally ends up entangled in a plot to make her the bride of the prince of the Cat Kingdom after she unknowingly rescues him from a truck. The longer she stays in the kingdom, the more cat-like she becomes. Several other characters help her along the way, most notably Baron and Muta (neko no ongaeshi).
It is an influential work in the furry genre in Japan.