The Bugle Call: Song of War. Volume 1: Mozuku Sora

A young bugler with supernatural powers is swept up into an epic struggle for the fate of the world. Cry havoc and sound the song of war!
In Arboral Year 1294, the world is dominated by nine massive towers known as the Spires—remnants of an advanced civilization, they are filled with lost secrets and powerful knowledge that nations struggle to possess. Luca is a bugler in a mercenary company who wants nothing more than to leave the battlefield behind and become a true musician, a maestro. But marked as one of the enigmatic Branch-hexed, and gifted with the strange ability to see the sound of his instrument, Luca finds himself drawn reluctantly into a war of epic proportions!
Left for dead after a battle, Luca is saved by the mysterious Pontiff and learns he is not the only person with unusual powers. The Pontiff has formed a special team of Branch-hexed individuals he plans to use to help him defeat rival empires—and Luca learns that his powers, rather than being an escape from the battlefield, now force him to be a muse of massacre.