Meiyaku no Leviathan  

The Leviathan of the Covenant, 盟約のリヴァイアサン

Twenty years have passed since the dragons returned to Earth. Flying high in the sky and leaving a path of devastation behind them, these creatures attacked humans without any apparent motive other than their destructive tendencies. In response, humanity took action. They delved into the practice of magic as a means of combating the dragons.