score:2
If you research on the Internet and have decided the brand, features (e.g. Unlimited data usage, throttled speed vs. limited data usage, unthrottled speed) and the budget, you can head straight to the listed retailer after arrival.
Related: How can I find the cheapest prepaid SIM card for a given country?
Take the free shuttle bus after you have cleared the customs and immigration.
Some airlines might sell SIM cards in their flight. If it fits your requirement, you might just buy from them.
There are mobile phones rental, pocket Wi-Fi rental, SIM retailers and vending machines in both terminal 1 and 2 at Narita Airport.