For SIM cards:

Please refer to Docomo’s official site for the service coverage area:
Docomo Service Area (Website in Japanese Only)

For Pocket WiFi:

・For 5 GB or 30 GB plan: 

Please refer to Softbank's official site for the service coverage area:

Softbank Service Area (Website in Japanese Only)

・For UQ WiMAX (Unlimited plan):

UQ WiMAX Service Area (Website in Japanese Only)

If you have trouble looking up the service area in Japanese, please feel free to contact us here.