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Should we have a baby soon? Life had stabilized, and my wife and I were working hard every night to have a baby. One day, her younger sister, Fumino, came to stay at our house for five days. We continued our acts as a couple, thinking that we should be careful, but it seemed that she was making noises and Fumino couldn't sleep. After that, we became more aware of each other, and we started having sex without my wife knowing. Gradually, the number of times increased, and all the sperm that was meant to be used to make a baby with my wife was used for her sister, Fumino.