Responsible for Shirahamazaka High's vocal club, who is put in charge of Konatsu's choir club after its advisor, the principal, is hospitalized following a bicycle accident. She is often harsh towards Konatsu, seeing music as something that should not be treated like a game. She was Mahiru's friend in high school and has not been able to get over her death.
She was the writer of the song "Melody of the Heart" and became a music teacher because of her love for music. Near the end, she starts getting over Mahiru's death and starts seeing some of Mahiru in Wakana, who appreciates Naoko's help and guidance.