Nao -Joshuu Ryoujoku Bou-

A Far East prison is built during the war. Female prisoners there are forced to work hard every day. Nao Kamijo is a former secretary-general who sentenced to jail for attempted murder and brought to this facility. It begins with the physical examination of shame, but various sexual harassments repeat over and over under pretext of what officers call "prison work". Her spirit gradually wanes till a certain encounter that changes her mind.

[From vndbreview]