Kazuya Kagami has a dream about a mysterious Amasogi. In order to deal with the Amasogi at school, Kazuya and Kiriha Obina make a club with class' 2-2 classmates (Shirou Shiramine, Osamu Osanai, and Chisato Chikaishi). They investigate the cause of girls' underwear gone missing at school. Another group of students is involved in activities with a Tsukumogami (spirit that has transformed after many years, obtaining a body and soul indistinguishable from a human's).