Riding the train is usually a simple matter, but not for a certain young man who is struggling to keep his hands off of a curvy high school girl with an extremely short skirt. However, when the train suddenly enters a tight curve and the man manages to cop a feel, the girl grabs him by his necktie and... offers to let him keep groping her in exchange for money?!

Chikan-ya-san follows two young people and their slowly escalating venture on the train.