Sacrament: Hunters of the Summoned

Summoned into a world of magic, wild beasts and countless wars, they were welcomed as heroes. Some of them remaining in their prior bodies, some reborn into new ones, but all granted immense strength and capabilities. Yet, there is nothing heroic about them. Most don't view the inhabitants of their new world as humans, but rather like characters in some twisted game. They only act according to what profits them the most, which is the only reason that the kingdoms have some sort of control over them. While fulfilling their missions, they slaughter countless of innocent people for the pettiest reasons.
Among the countless victims of their crimes is Echo, a young adolescent boy. Driven into despair, he vows to himself to put a stop to this, put a stop to them. He will become a hunter of the summoned!