I visited Japan with JY a couple of years ago and there is a review on the review section (currently bottom of page 2) and this includes a bit about money.

I had been in Japan previously so already had the usual array of fridge magnet souvenirs etc so cash was just for day to day spending.

I am a bit "old school" and prefer to pay for everyday spending in cash and not pay for a coffee or whatever on a card. Also having cash, for me at least, means you are not at the mercy of finding the nearest cash machine! Most places accept cash and, as I recall, one or two restaurants insisted on it. Anything more specific then feel free to ask.

Ian