Mamoru is invited by his stepmother Yui to accompany her on a shopping trip. Their bodies are pressed together against each other on the packed train. His lower body heats up with each movement of the carriage as he thinks of the beautiful Yui. His erect cock is thrust between Yui. He thinks Yui will get angry, but she surprisingly starts stroking his cock, saying, "We haven't done it recently." He refuses, saying it would be bad to do it on the train, but Yui ends up raping him in the Yui at the next station. He can't forget that cock, and Yui starts craving it at home too.