Chikagi Katsuragi enters Kagamisaki High School with the firm intention to have a quiet school life, but not if her hyperactive classmate Hino Hibiki has something to say about it! Chikagi is fighting a losing battle, as she happens to be the younger sister of the wonderfully eccentric former Student Council President Chidori Katsuragi, and that alone assures that her high school life will be anything but quiet!