「ヤヌスの鏡 ～VF文庫ADVANCE～」

Tomomi is an ordinary girl working at a family-style restaurant.
One day, she is suddenly taken to a different world.

She meets a few beautiful women in the darkness.
But they are carted off by monsters in front of her...... Right before she gets caught by the monsters, she manages to escape from there and ends up wandered off into an underground maze....
She tries to escape from the insane maze.
On the way to the only exit, she finds the beautiful women being chained in rooms and humiliated by the monsters...... The castle she is in is there only to have human beings to be pregnant monster's babies to keep the tribe populated.

[From DLSite English]