Starting July 24, 2015, prepaid SIM cards are now available for overseas visitors at the arrival lobbies of Narita International Airport. Sold via vending machines, the SIM cards require only credit card payment, and may be purchased 24/7. This means that visitors on late night and early morning flights may now use their own devices directly after arriving at Narita.
The locations of the vending machines are on the 1st floor, Main Building Central Section Terminal and 1st floor, Main Building Central Section Terminal 2. The SIM cards come in 3 different sizes to suit a wide range of devices, with usage limits of 100MB per day. They are available for 7-day and 14-day periods.
For more information, please visit these websites.