Originally Posted by
jpatokal
They're not concerned with identity, since purchasing prepaid SIM cards with foreign passports is explicitly forbidden.
It is not forbidden to buy a prepaid SIM card just because you are a foreign passport holder, as far as I have read. It is just not permissible to buy a prepaid SIM card without acceptable proof of address in Japan and a proof of identity, and if you need an alien registration card if you are a foreign national. It does not mean that you are forbidden from buying a sim card just because you are a foreign passport holder.