I recently vacationed in Japan (October of last year), and IMO even in the last couple of years credit card use has become more widely available. If you have a travel credit card, you should be good to go in more touristy, urban places. Wander out of the city though, and you'll absolutely want some cash on hand.
I actually do recommend getting it from your bank, with about a week's worth of lead time. But please note! Different banks will have different exchange rates-- my bank, BoA, gave me a pretty good rate and I converted about 1.2k with maybe $10 lost in the conversion. My friend with Citibank got ripped the hell off. If you're traveling with anyone, or have access to multiple banks, perhaps go "shopping" around a bit and see what your options are. I understand you can do the conversion in the airport, or after you land, but personally I don't like not knowing exactly how much and what the conversion rate it until I get there. Maybe save that for a last resort if none of your banks offer good conversion rates.
The yen is very weak right now, so this is actually an excellent time to go.