Tate Yuuichi has just transferred to Fuka Academy and is thrilled at the prospect of living in a normal co-ed environment. Little did he know that he enrolled in a school where all-out battles between female students are nothing out of the ordinary! On his first day Tate unwittingly stumbles into the middle of a fight between Mai and Natsuki – two of the ‘HIMEs’, a group of specially selected and powerful girls recruited to fight monsters known as Orphans. While the HIMEs themselves are strong, they can only unlock their true power when they partner up with their ‘Key’. Unluckily for Tate he finds that he is not only the Key for Mai but also Natsuki! Now Tate is entering a world of monsters, battles and even rival HIME groups, but that’s only the start of his troubles…