Second Lieutenant Yuu Mononobe transfers to Midgard Academy, a school that trains girls born with dragon-derived 'D' powers to fight the monsters that emerged twenty-five years earlier, and finds himself the only male student there. His older sister Mitsuki serves as student council president, but it's classmate Iris Freyja, struggling with her own D training, who pulls him into academy life as he adjusts to a campus built entirely around abilities he doesn't share. This manga adapts the Unlimited Fafnir light novels.