Cash is king in Japan - Travelex

At more and more places you can pay with credit card in Japan but as soon as you go to local markets, many restaurants, nightclubs, small shops etc you will have to pay with cash. As Japan is a very safe country you should not feel uncomfortable having cash with you.
You should bring some Japanese Yen with you from home to be on the safe side. At 7Eleven or at post offices you can make cash advances. It is very easy!
If you bring cash you have to find an Exchange Office were you can change your money to Japanse Yen. Travelex is the biggest company but they are really not everywere. This one is at the the Shinagawa station in Tokyo. Remember that they are only open office hours!