Our telecom partner in Japan is KDDI and the data connection works in « 4G/LTE only » mode in all areas.
Your Transatel DataSIM card will work only if your smartphone can be set to « 4G/LTE only » mode (please refer to the manual of your smartphone).
If you want to be sure to get a connectivity in this country, we recommend you to use your SIM card in another device like a LTE Wi-Fi hotspot (sold online), a laptop or a tablet – these devices are configured as « 4G/LTE only » mode by default.