Law / Rule, Tokyo
You need to check carefully any over-the-counter medicines which maybe commonly used in the U.S. or other countries, into Japan. Some of these you might not think twice about but they are not all allowed and Japanese customs can be very strict about this. Most doctors in Japan however can prescribe something similar to any you find banned to get you through your trip.
If you have any prescription medication, you should consult your local Embassy or consulate prior to departing.
In Japan, we are not allowed to use our mobile in the subway and train. No punishment once caught. The main reason passenger not encourage to use the mobile is, there are increasing of patient of heart attack in Japan, and all of them use a pacemaker to control their blood circulation. The usage of a mobile may disturb the counting and this may give the patient a hard time.
I made the mistake of attempting to photograph the koban in front of Shibuya Station. An officer noticed me and immediately gave me the "crossed arms" in the air, and came running over. Apparently, they don't take kindly to being photographed.
Other than this one incident, the Japanese police have been nothing buy polite and very helpul.