Sentenced to Be a Hero, Vol. 1 (manga)

Hero: a title that carries the most severe punishment a criminal can earn. Why? Because these "heroes" are the front line in humanity's war against the Demon Blight. Driven mad by centuries of fighting, the penal hero forces are made up of the most morally bankrupt to exist throughout history. They fight without hope of redemption, driven mad at the helplessness of their mission as the fallen are resurrected to continue struggling for all eternity. It is to this chaos that Xylo Forbartz-former captain of the Order of Holy Knights-is sentenced for his crime of deicide. But after he encounters Teoritta, an unknown Goddess of the Blade, the two will forge a pact with the power to change the course of history, and maybe save the world from annihilation...