Tatsuya, the son of mother Fumie and father Koji, had secretly watched his parents' nightly encounters since childhood. What he saw was far beyond normal—fierce, intense acts unlike anything in other households. Fumie's plump body tightly bound by rough rope, her expression a mix of ecstasy and pain. Each time he watched, Tatsuya felt a dark desire growing inside him, which he desperately tried to suppress. But eventually, his restraint reached its limit, and he resolved to assault Fumie. She resisted at first, yet as her beloved son tied her up, she gradually awakened to passion, responding to his advances and becoming aroused herself.