One day, while cleaning the windows, Ichika lost her balance and nearly fell off her chair. Her son supported her just in time and saved her, but what he grabbed was Ichika's big, plump buttocks. From then on, the son could not forget the feeling of Ichika's buttocks pressing heavily against both his hands, and he began to follow Ichika's buttocks with his eyes. Then, the son began to have obscene fantasies, and one day he could no longer hold back...