Yuuichi Tate is thrilled to be attending a brand-new high school. However, he soon discovers that the school he chose is frequently attacked by strange creatures known as ''Orphans''. To combat these invaders, the school has established a special task force composed of female members called ''HiME''s, who wield various elemental powers. But there is more to it. Each HiME possesses a unique ''Key'', another individual who, once found, can partner with the HiME to form a ''Child'', a combat unit essential for effectively fighting the Orphans. Given Yuuichi's luck, he finds out he is not merely the ''Key'' for one HiME, but for two... two highly competitive, rival schoolgirls. And that is only the beginning of the trouble.