Hi PaulineD,
Whenever I travel, I use the plug that comes with the charger and the correct adaptor that will fit into the wall (in your case it'll be two flat pins) and I have never had any problems. I can't imagine there being any problems in Japan with regards to charging your devices, but if there is I am sure your Tour Manager or your fellow travellers will be able to help you out if necessary.
Kindest regards,
Monty
No, there shouldn't be any problem: I took my iPhone, MacBook Air and Nikon camera with me to Japan last year (Tokyo - Matsumoto - Takayama - Kanazawa - Hiroshima - Kyoto) and used the respective supplied chargers with '3 pin UK' - to - '2 flat pin JP' converters, and I don't recall having problems charging any of the devices.
You'll enjoy Japan - it's a fascinating country!
Jim