Currency exchange services are available at major banks, currency changers, big hotels, and certain stores.
https://www.mizuhobank.co.jp/tenpoinfo/gaika_ryogae/index.html
Cash withdrawal and cash advance services are allowed on major credit cards or cash cards with the PLUS and Cirrus marks. You can withdraw Japanese yen at ATMs in post offices, 7-Bank ATMs found in 7-Eleven convenience stores, and in airports. There are also certain ATMs in banks such as Citibank and Shinsei Bank that will work.