Hikaru has lived a life where he and his younger sister support each other. When his sister finds someone special, he decides to leave home, but is persuaded to stay and now lives happily with his sister and her husband. One day, after working overtime, he is lulled into a doze by the swaying of the train. Hearing heavy breathing, he wakes up to find his sister's husband stroking his cock while peering up his flipped-up skirt...