Kuroinu Kedakaki Seijo wa Hakudaku ni Somaru 

黒獣 ～気高き聖女は白濁に染まる～ オリガ×クロエ 黒の城、崩落編
 

An epic battle was taking place for more than several hundred years between two countries. One of them sent a special troop, but the soldiers went over to the other side and started invading the country they used to belong... Also, they declared the foundation of nation. In the country, all women had to serve all the male visitors sexually...