Juuou Mujin no Fafnir

Japanese Title: 銃皇無尽のファフニール

English Title: Unlimited Fafnir

Plot
With the sudden appearance of the monsters that came to be called Dragons, the world had completely changed twenty-five years ago. Before long, within the human race supernatural girls with the power of the dragons, called D were born. The secret existence of the only male D the boy Mononobe Yuu, was forcefully thrown into the school where the girls of D gathered Midgar, where he saw the naked body of one of the students, Iris. Furthermore, meeting his long-lost sister Mitsuki, Yuu seems to have been enrolled into this school..."When there's really no other choice, Iris, I will kill you. Can I really... believe you The curtains open as the one and only story about the boy who was supposed to become the strongest assassin and the incompetent girl unfolds.