NTT DoCoMo SIM Cards only work on phones that support minimally Band 1 LTE.
Please search on Google or your device manual to check if your phone supports the LTE Bands used by NTT DoCoMo.
You can use FrequencyCheck.com Website to check your device compatibility with NTT DoCoMo’s Network.
Kindly note that MOST Budget and China-branded phones (i.e. Xiaomi, Meizu, Huawei etc.) do NOT support Band 1 LTE.
Please purchase the Softbank SIM Card your phone does not support at least LTE Band 1.