Your girlfriend, Mirai-chan, is a bright and a little bit of a girl. She was forcibly taken to her parents' house, and what awaited you were her sisters who were full of sex appeal. A sister who squeezes sperm in the vagina one after another in front of her sister. Eventually, the dispute between the sisters heats up, and your testicles will be in full operation while you are staying at your parents' house.
