JK to Orc Heidan: Aku Buta Oni ni Ryougyaku Sareta Seijo Gakuen

Anime adaptation of the PC game by Blue Gale LIGHT. Deep in a forest, there existed an old European-style building made of brick. It was an all-girls' school attended only by girls from good families. One day the school was covered by a mysterious thick fog caused by an earthquake. Orc soldiers emerged from the ominous fog. The schoolgirls were attacked one after another by these brutes from a parallel world. The girls' resistance was futile; they were crushed by the powerful orcs. Rape and death, only tragic screams echoed through the school. Why did it become like that!? There was no one who could answer that question... (Source: VNDB)