I think in Japan the best way to have mobile Internet is to get a tourist SIM card from the airport. I do not recall the price, but I remember I had considered them fair. They might not be compatible with your phone though. The problem is with the supported bands and there is no way to fix it. It either works or it does not.
If you do not want to stop using your current SIM card or if you have an incompatible phone, you can rent an “egg”. It is a small mobile hotspot that your devices connect over WiFi. It is also useful if you are a group, because multiple people can connect to it, so you just get one.
If you do not want to stop using your current SIM card or if you have an incompatible phone, you can rent an “egg”. It is a small mobile hotspot that your devices connect over WiFi. It is also useful if you are a group, because multiple people can connect to it, so you just get one.