I guess many tourists from abroad have mobile internet problem. You might want to use Google map, Facebook and other apps with their iPhone, tablet or smartphone. However there are few free WIFI spots and mobile phone roaming is very expensive in Japan. Recently, new mobile servicers provide reasonable sim cards for tourists. If you have sim free smartphone, you can use them. I’m going to introduce 4 choices (for your sim-free mobiles) which are quite suitable for short stay in Tokyo.
1. Japan Travel SIM powered by IIJmio (IIJ) 90 days, 2GB, 4000JPY, 4G LTE, IIJ is first internet provider in Japan. 2GB is enough data size for 90 days. This is suitable for all tourists. You can buy it in airport, Bic camera, Sofmap and Yodobashi camera. Actually I recommend this sim card because the cost is reasonable and the network is strong. If you want to more detail, please go to the URL.
2. OCN mobile ONE Prepaid SIM for VISITOR, 30days, 100MB/day, 3980JPY, 4G LTE OCN is provided by NTT group. You can use high speed internet for 100MB. After 100MB, the speed will be slow, 200kbps. But you don’t need to mind the data limit. Next day, you can use high speed internet again.
3. PAYG SIM (b-mobile), 7days, 3GB data, 60 minutes call, 9980JPY, 4G LTE b-mobile is one of the famous mobile company in Japan. They provide nano sim, micro sim. They provide 7days sim card. It is suitable for short stay traveler. You can buy it in Yodobashi camera (Big electronics shop) and airport.
4. Prepaid LTE SIM (So-net) Plan 100M: 30 days, 100MB, 3000JPY, 4G LTE Plan 500M: 60 days 500MB, 5000JPY, LTE, Charge: 200MB/1500JPY, 500MB/2000JPY, 1GB/2838JPY, So-net is offered by Sony. This sim card is for long stay travelers. If you need more data, you can charge it online with credit card.
I hope the information will help for your great sightseeing! Please check it out!