MIAA-172 Yui Nagase serves as maid to shield her sister from their adoptive father, who takes advantage of her devotion

A woman is adopted into a wealthy household alongside her sister. The adoptive father mistreats the sister, but shows lewd attention to the other. To protect her sister, she takes a maid role, and the father exploits her protective feelings. He repeatedly violates her, and her delicate body gradually breaks down as she loses her sense of reason.