Kokomi Naruse is a high school girl preparing for her entrance exams. Every morning on her commute bus, she is suddenly subjected to molestation. It always happens just before her period, when her body becomes especially sensitive. Terrified and humiliated, she finds herself powerless to resist, yet gradually captivated by the man's skilled fingertips. As the molestation grows bolder, Kokomi is forced to endure it helplessly—while secretly awakening to the pleasure she feels.