Just an FYI (I spent a year in Japan): You will not be able to get a SIM from any of the carriers in Japan without a visa that is valid for MORE than 90 days. You can rent SIMs at the Airport, but pretty much nowhere else, and none of them are the micro SIM size. You return the rental SIM when you are finished with it, so if you cut it down to size you will get charged for damage.
For prepaid and contract SIM or phone purchases by foreign nationals, Japanese phone companies take photocopies of your visa, entry permission sticker, and passport photo page and fax them to their head office for verification with immigration, so there really isn't a way of talking your way into them giving you a SIM, even if you speak Japanese.