Kae Horii (Erika Sawajiri) moves into her new flat in an undisclosed area of Kyoto. While unpacking her belongings, she discovers a hidden compartment behind a inconspicuous mirror. In that compartment, Kae finds a notebook, that turns out to be a diary belonging to the previous tenant. Later that evening Kae starts to read the diary. The writer of the diary is Ibuki ...