The school uses the fictional sœur system where any second- or third-year student, the "grande sœur" ("big sister"), might pick a younger girl who will become her ""sœur"" ("sister" in French). The "grande sœur" gives her the "petite sœur" ("little sister") a rosary and promises to look after her and guide her. The basic etiquette demands the "petite sœur" to call her "grande sœur" ""onee-sama"" ("older sister" in Japanese). Aside from being used in prayer, the rosary is the instrument that certifies the "sœur" union and relationship between two students. There is an implicit code of behavior between "sœurs", especially in the Yamayuri Council—the student council of the school: quietness, measure and respect towards each other; values deeply attached to traditional Japanese education.