Fifty years ago, mysterious creatures known as the "Huge" suddenly appeared all over the world, posing an existential threat to humanity. To defend against these menaces, soldiers in the form of teenage girls known as "Lilies" use the energy of magie within their bodies to power weapons called "Counter Huge ARMS", or CHARMs. After being saved by a Lily two years ago while evacuating from a Huge attack, Hitotsuyanagi Riri vowed to become a Lily herself. She enrolls in the prestigious academy of Yurigaoka, a training ground for Lilies, in order to be reunited with Shirai Yuyu — the Lily who rescued her. Much to her confusion, however, the person she thought to be cheerful turns out to be quite antisocial and prefers to fight alone. Even so, Riri still wants to get close to Yuyu and is willing to do anything she can to reach that goal.