Yuu Mononobe, the only known male D, is forced to enroll at Midgar, the all-girls academy where girls born with dragon-like powers are gathered, twenty-five years after dragons scorched the world and vanished. On arrival he stumbles onto a student named Iris Freyja mid-change, and she attacks him on reflex. Alongside Iris and his adoptive sister Mitsuki, Yuu trains to keep the D's from turning into dragons themselves and to learn why the creatures disappeared.