Just FYI, there's another thread that's been resurrected by someone else about Chase Sapphire cards not working. Those are the Chase cards I'm talking about. My wife and I tried both of ours multiple times.

This is also the card I was referencing when I said some cards should work, but don't for whatever reason. I'm guessing whatever hardware a lot of stores/restaurants use in Japan won't read metal cards. We literally watched with our own eyes about 8 or 10 different places try to swipe multiple times and the mag strip seemingly not being read. They swipe and swipe and nothing comes up. This has never once been a problem for me in the US.

Usually in those cases, AMEX works. But sometimes, they think it does initially, and then it doesn't in the end. Some stores still only accept Japan-issued cards, including AMEX cards.

No card we've tried has been foolproof, and some places still only accept cash anyway.

Granted, the more touristy places generally accept foreign credit cards (although again, not my Sapphire card). If you're mostly going to be going to Tokyo Tower and SkyTree and the Park Hyatt, you'll be able to use a US credit card of some kind. But don't count on it if you're planning to go to the garlic restaurant in Ebisu (for example), or anywhere outside of the major areas of Tokyo, or even a lot of non-7-11 convenience stores.

In terms of ATM's, 7-11 is really the only ATM to even bother with. Maybe it depends on the bank, but with a Chase account, my wife and I have wasted entire days trying different ATM's with no luck at all. Only 7-11 works reliably. The nice thing is 7-11 has ATM's outside 7-11's too, such as at the T-CAT bus station in Tokyo. So it's not that hard to find them, and you won't ever be that far away from cash. I'd just recommend having a pocket wi-fi with you so you can always get online and find the nearest 7-11 ATM.