Hi PerfectBlue97,
I have found a little snippet from the GOV website which may be of help...
Japanese post offices, 7-Eleven stores and Citi Bank have cash machines, which will accept some foreign cards during business hours. Cash machines at banks and post offices generally close at 9pm or earlier and may not operate at the weekends or on national holidays, however, ATMs in convenience stores and some shopping centres are available 24 hours a day.
I doubt there will be many places that that give cash back, but there will be an opportunity for you to replenish your cash from an ATM or alternative source. If you mention it to your Tour Manager, they will be more then happy to help.
Kindest regards,
Monty