My Big and Horny Sisters

Synopsis

Based on the erotic game by Marine. On March 22, a Saturday during summer break, Shun is told to go back to his Nee-chan's home to take care of something. Shun suspects he might be turned into a toy by his Nee-chan. When Shun arrives home, Nee-chan explains that they have contracted an unknown disease called Idiopathic Estrus Syndrome, which causes his sister to experience an uncontrollable heat in her body. The only way to cure the disease is through regular intake of male sperm. Thus, the romantic relationship between Nee-chan and Shun begins...