Yuu's the only male D in a world that doesn't know he exists, which immediately puts him in every conversation about power that actually matters. The show plants a real mystery in his past, a memory mechanic that actually explains why he's different, and refuses to let it be window dressing. It executes the harem formula without pretending to be anything else, giving each girl a reason to be there beyond "cute."

Twenty-five years ago, monsters called Dragons appeared without warning and changed the world. In their wake, girls began to be born with dragon-like powers, able to create dark matter and shape it into weapons. These girls are known as D. Yuu Mononobe is the only known male D, and he is made to enroll at Midgar, an academy for D girls who learn to turn their abilities against the Dragons. There he has an awkward first encounter with Iris, a troublemaking classmate, and finds his little sister Mitsuki, from whom he has long been separated. Yuu must build bonds with the girls around him and fight alongside them against the Dragons threatening the world, in an action fantasy with romance and ecchi elements.