The moans of his mother, Reiko, could be heard coming from his parents' bedroom. Kosuke was flustered by the voice, which was so erotic. His friend had said that he was shocked when he got a glimpse of his parents' sex life. But inside him, intense emotions welled up that he couldn't suppress... Those emotions were jealousy towards his father, who was making his mother moan in such erotic sounds. He wanted to possess his mother's love all to himself. And the forbidden desire to fill his mother's vagina, which had already been filled with his father's sperm, with his own sperm.