The 6th and 7th Squads join forces to rescue Yuuki, who was kidnapped by his long-lost sister, Aoba. Upon learning of the circumstances of her and her allies, Yuuki tries to convince them to let go of their hostility toward the Demon Defense Force...but the conflicting ideals of the two groups inevitably lead to a fierce battle. With girls on every side fighting over him, can Yuuki find a way to mediate a cease-fire before it's too late?!