Vending machines for SIM cards will be available at Narita Airport starting July 24th, allowing foreign visitors to get connected right upon arriving in Japan.
The "Prepaid SIM for Japan" cards, which are also available at Kansai International Airport, can be used for either 7 days and 14 day periods. A one week SIM is priced at 3,450 yen, with the two week SIM priced at 4,950 yen (consumption tax of 8% excluded).
This prepaid SIM can be purchased only by credit card (Visa, Master Card, JCB, American Express, Diners Club), meaning you won't have to exchange currency beforehand. A maximum of 100 Mb of data can be used per day, with a download speed of 150 Mb/s and upload of 50 Mb/s.
One vending machine each will be installed in the Arrivals lobby of Narita's Terminal 1 and 2, and services will be available in English and Chinese. In addition to SIMs, the vending machines will also offer smartphones and other mobile phone-related accessories such as routers for sale.
Before making a purchase, users must register their personal information. This can quickly and easily be done by scanning your passport on the touch panel built into the vending machine.
Official Press Release (in Japanese)
"Prepaid SIM for Japan" official website (in English)