OL Mayu, who commutes by train every day, works late into the night and takes the last train home. One evening, exhausted from work, she falls asleep on the train and a man across from her sees her crotch. The woman gets excited from being seen and masturbates at home. She thinks to herself 'If I do it secretly...' so she removes her panties and starts masturbating in an empty train car. One night, she is seen by a man and they enter into a strange relationship where they mutually masturbate. The woman beckons the man to lick her crotch. The excited pair have secret sex on the train.
