7:30–9:00 AM and 5:30–7:30 PM on Tokyo's main loop line is physically packed. Travel outside these hours if possible.
If you must travel in rush hour, expect to be pressed against strangers. White-gloved staff sometimes push commuters in to close doors. It's surreal.
The Marunouchi, Hibiya, and Ginza subway lines have slightly different peak windows. Check Google Maps for less crowded alternatives.