Dan Oniroku: Ikenie shimai(1987)

The pinnacle of Oniroku literature!! Tormented!! Massive humiliation and extreme pain transformed the sisters into females.

When the elderly owner of a luxury inn passes it is left to the staff instead of his two daughters. The staff make plans to sell the inn to a gang of yakuza. But the gang sees profit in the daughters as well and brutally conditions them for sale.