Juuou Mujin no Fafnir

The emergence of creatures known as dragons drastically altered the world. Soon after, individuals known as "D" appeared, possessing supernatural abilities tied to these creatures. Mononobe Yuu, the only male "D," is forced into Midgard, a school housing female "D" students. There, he witnesses a classmate named Iris in a state of undress. Later, he encounters his estranged sister, Mitsuki, and finds himself enrolled at the school. Tension arises between Yuu and Iris, with Yuu declaring he may have to kill her if necessary. Doubt lingers in Iris's mind regarding his words. The story follows Yuu, who was destined to become a top assassin, and his complicated relationship with Mitsuki.