Japan is still a little behind in the use of VISA and electronic payment cards in general. You can eventually use your payment card in most places in the big cities, but if you go out into the countryside, inaka , then cash is still necessary.
In Japan it is a good idea to carry cash. You can raise i konbini machines such as at e.g. 7-Eleven, so just raise a good chunk of money at a time. You often get around DKK 30 withdrawn from the ATM every time you withdraw.
If you want to bring some money from home, you can order Japanese yen from your bank. It takes about one or two weeks for most banks to get them home, so remember to order well in advance.