In 1992, a girl falls from the rooftop of a middle school. Beside her dead body was a cassette recorder, still recording... 32 years later, Honoka is hired to teach summer classes at the same school. One day, she hears humming from the rooftop and the voice that shouts, "Listen to my sound!" followed by a thud of a student`s body. Honoka and two students become suspicious that the two accidents are somehow connected. They look into the yearbook from 1992, and find a picture of Sana, their classmate who is obsessed with collecting "everyone`s sound" to write her song. They soon realise that Sana is the cause of the accidents, and anyone who hears her song can be the next victim.