My exgf's daughter came to visit a few years back she didn't have a credit card as she was 19 at the time, so they got a prepaid mastercard somewhere in the US and that worked well for her. I can't remember her having any issues.
16 years ago when I came to Japan often I would have issues using my regular US credit card in Japan, that problem is long gone, so I suspect any old card from the US will work, but you should still bring a significant amount of cash for use in small restaurants and cafes where cards aren't generally accepted.