Yoshioka Haru (voiced by Chizuru Ikewaki) is an ordinary and somewhat confused female high school student. One day on her way home from school, she accidentally saved a kitten that was almost killed by a car. Who would have thought that the kitten would stand up and thank the girl in a human way. What Koharu could not have imagined was that her unintentional act of kindness changed her fate. It turned out that the kitten was the prince of the Cat Kingdom. In order to repay Koharu's kindness, the Cat Kingdom launched a ridiculous act of gratitude, but the mice they regarded as "superior" made Koharu laugh and cry. Not long after, Koharu accepted the invitation of the kingdom to visit, and during the period, she agreed to become the prince's concubine without knowing it. The girl was about to completely turn into a cat, and the mysterious baron (voiced by Yoshihiko Hakamada) became her life-saving straw... This film is also regarded as a spin-off of "Whisper of the Heart".