Mai Nadasaka, a piano teacher, visits her student Makoto's home to provide careful instruction. Makoto's mother passed away several years ago, and since Mai bears a striking resemblance to her in both appearance and demeanor, she is often mistaken for the deceased mother within the household. Ever since Mai began playing the piano at the Hattori residence, the entire family has grown increasingly convinced that she is their lost mother, showering her with abnormal affection as if she were truly that person. As a result, Mai becomes more and more confused, forced to question her own identity and position within the family.