Message from SoftBank
Your device is connnected to the carriers with non-Data flat-rate.

How to enable "Data Flat-rate service"

To use data communications at flat rate (0 to 2,980 yen / 1 day * Japan time), you must connect to the "Data Flat-rate service" applicable carriers.
Please select the applicable carriers manually in the network setting.

How to find the "Data Flat-rate service" applicable carriers

Please check SMS you recieved.
For example, SoftBank/44020/...

"Global Roaming Packet Flat Rate" details

See details of "Global Roaming Packet Flat Rate"

*Accessible only via iPhone, iPad, Smartphones, and Tablets.

When you don't need data communication

You must turn off mobile data communication and 4G setting.

E[Enable 4G] > OFF
E[Cellular Data] > OFF

*Handset display will vary depend on the handset.