An older brother desperately wants to date his younger sister, Miiro. But his younger sister hates him because he always takes secret photos of her and confesses his feelings to her. One day, Iroha breaks up with her boyfriend and accepts her brother's confession, saying, "If it's just for a month..." She doesn't know that this will be the start of a forbidden relationship from which there is no turning back. From that day on, they start living an incestuous life that they can't tell their parents about. Gradually, Iroha becomes captivated by her older brother and can't live without him. After a while, her older brother leaves home and suddenly returns with his fiance... At that moment, Iroha...