:LOOP ~Izanai no Kaikiten~

The two young Kodama sisters, Nozomi and Hikari, decided to go for a drive in the countryside, to celebrate the end of Nozomi's brilliant high-school year. They get lost in the woods and are greeted by a handsome young man, who offers to bring them to the nearby mansion, known as the Deer Garden Temple, and to spend the night here. The exciting adventure soon turns into a nightmare, when the inhabitants of the mansion make Nozomi to their sex slave...

[from Moby Games]