Fuuka's piano playing is not progressing well, and the stress caused by this leads to bedwetting. At first, she was very resistant to wearing diapers because she felt embarrassed and miserable. However, after changing into a new diaper, she realized that the sense of security and softness was comfortable. Now she even looks forward to wearing diapers when she goes to sleep. She is a character named Fuuka in the movie "Lonely Castle in the Mirror". It's a great movie, so if you have the chance, please check it out.