The information has been confusing about this, I thought they only accepted cash.
Right outside of customs, as soon as you exit you can:
1) go immediately to your left and exchange cash for yen. They do not accept credit cards. There is an ATM to withdraw cash, but IMO either bring cash with you to exchange or get yen from your bank in advance.
2) You can buy a Welcome Suica card with a credit card (you don't have to pay cash!). You can load up to 10k yen on a card, and you can buy multiple cards.
After you exit customs, look for the monorail sign. Go towards it like 100 feet, and to your left will be a line of people waiting to buy Suica cards. Super easy.
by Battle-Chimp