Momo is a princess of a magical world that has come to Earth together with three companions - a bird, a dog, and a monkey - to help humans regain their happiness and bring the two worlds together. She has the appearance of a pretty, cheerful teenage girl, and immediately attracts the attention of a young boy who lives in a quiet town with his biologist father. Together, the two must solve the mysteries of the town, and perhaps find happiness for themselves as well.