I am very sorry but it is not easy to get good stable free wifi access in Japan especially in the countryside. Here is the one solution that would help you to get Mobile wifi during your stay in Japan. You can apply on online and get the device at the airport/Hotels or where you stay in Japan. Click pictures to get more info!
Have a Japanese phone number in your country If you want to have a Japanese phone number(Not mobile), even if you are in the outside of Japan, This is the one solution that you can have a Japanese phone number in your country or or for your virtual assistants in Japan. I can help you to set up the system. Click here to get more info