Although they are brother and sister, they have always been instinctively attracted to each other. However, this is a faint love that will not come true. Before they know it, they become aware that they are a man and a woman, but each of them uses their rationality to refrain from interfering with each other. However, on his brother's 20th birthday, his parents reveal that the two are actually step-siblings. My sister happened to hear about it. Late at night, after she was asleep, her sister came alone to her room... Now