The overcrowded trains of Tokyo have been a well-known dirty old man's delight for years. To try and deal the chronic groping problem, about ten years ago the rail companies re-introduced an old idea of women-only cars at peak hours on certain lines.
Most are grateful for the safe haven and don't think there are enough, a few see it as a band-aid solution and not facing up to the real problem. All I know is you feel like a right perve if you ever accidentally get into one of these cars during the Women Only hours as I did once when when I first got here without knowing the rules… it was a long couple of minutes to the next station.
It still goes on though and enterprising gropers (chikan) have even been known to feign disability, as there's an exception for the disabled who can ride anywhere.
A friend of mine was a real looker and used to get this shit on the trains all the time when she was younger. Some guy even called after her once, “thank-you”, as she made her escape to another car at the next station. She ended up carrying a hat-pin in her bag and sticking it HARD into any wandering hands that came her way. Nice one.