Kurogane Hayate finds herself in a dilemma. Her twin sister, Nagi, is recovering from an injury and needs someone to go to school in her place. Little did she know, the school was based on a "Swordswoman League," where everyone participates in what are called Duels for Stars with their sisters-in-arms, shinyuu, in order to gain prestige, money, and power.
Her first encounters with the students at this new school range from intimidating, such as with the Student Council President, Amachi Hitsugi and her shinyuu, Miyamoto Shizuku, to completely awestruck, such as the hot-headed but extremely experienced (and without a shinyuu) Mudou Ayana. At first Hayate thinks she can get away without participating in the Duels for Stars, but the first day she comes home, the orphanage she cares for deeply is a complete wreck...