The Sœur System (note: sœur is the French term for sister, and pronounced similarily to the English word sir) is used by Lillian Academy. In this system, the a second or third year student takes on a first year student as her petite sœur ("little sister" in French), thereby becoming their grande sœur ("big sister" in French).

The grande sœur teaches her petite sœur etiquitte and other skills, and offers them companionship and guidance. Though the relationship between sœurs is intended to be more of a platonic sisterhood, it often develops romantic undertones.