Isekai Senshu wa Kaerenai

You have been summoned to another world, where you must become a representative (fighter) of the demon king's camp and fight a proxy war (holy war) against the empire. It is said that they will give you training until the day of the war, but... This is a multi-end romance game with male and female characters, whose stories branch out as you become closer to them. The game contains some painful scenes depicting people being treated without dignity. [translated from Itch.io]