Imouto Jiru

Akira's father, an archaeologist, recently remarried. This provides Akira with a stepmother, Yukie, and three stepsisters named Yuki, Nana, and Miu. While on his honeymoon, Akira's father makes a discovery and remains at the site to supervise. Consequently, Akira is left at home with his new family. His situation becomes complicated after he is discovered in bed with Yukie. He subsequently finds a box containing an ancient scroll and three bottles. Drawing on his father's teachings, Akira deciphers the Sumerian text on the scroll. This act binds him into a contract with the goddess Inana. She instructs him to collect his sisters' love juices in the bottles before the next full moon. Failure to do so will result in a terrible horror befalling him.