Norika Minakami, a 23-year-old university student, had just alighted from a Tokyo subway train at the peak of Japan’s infamous morning rush hour. As usual, men and women were pressed up against each other on a sweltering July day.

Ms Minakami (not her real name) felt something brush up against her bottom, but thought nothing of it. Then it happened again – this time an unmistakable squeeze. She grabbed the hand of the perpetrator and dragged him out of the train at the next station, where she reported the incident to station staff and the police.