The film is set at a prestigious catholic school for girls called Lillian Academy. The school has a stored history as well as its own set of traditions which get passed down from one generation of students to the next. In keeping with this philosophy, a system is in place in which certain seniors choose a younger student to give their rosary to and then act as a big sister and mentor. After a chance encounter which leaves a big impression on first year student Fukuzawa Yumi (Honoka Miki), she's chosen as the "little sister" of the very prim and lady-like Ogasawara Sachiko (Haru).