For those who are visiting Japan via other countries, there are some options to bypass the high cost of Japanese SIM cards, the low data amounts, and the clunky profiles or custom settings some of the cards need. If you are stopping in Hong Kong, mainland China or Singapore (there might be other country options as well) prior to visiting Japan, you can buy a regional (all of Asia) or two-country SIM that will often offer either unlimited or a larger amount of data at a great price.

For example, I stopped in Hong Kong for a few days before arriving in Japan and bought a China Mobile 7 day unlimited Japan data SIM that runs on CMHK LTE in HK and Softbank LTE in Japan - US$24 and no special profiles, APN changes, etc - just reboot the phone on arrival in Japan and make sure data roaming is enabled and you're good to go. I didn't ask if the cards were activated at purchase, or when used in the phone, but if it's the latter, you could buy a few of these to stock up for future trips to Japan. They also may be available to order online.