I learned a fast and hard lesson recently. I was on my way to catch the Shinkansen (bullet train) from Hakata to Shinagawa (in Tokyo) in the wee hours of the morning and wanted to grab some cash. First I went by the local bank branch that I knew the location of but found that it wasn’t just the bank that was closed (not a surprise given the hour) but the ATMs were all off as well.
So next stop - the Convini [コンビニ] (the Japanese shortening of Convenience Store). But there I found not cash, but a bigger shock - the convini’s ATM would only service ATM cards from certain banks at certain hours. Admittedly, this is not very convenient.
For those of you who do not already know, Japan is very much a cash country. Meaning, that as you go through Japan there are many places that using a credit card is either difficult or outright not accepted. So in Japan, carry cash and probably a decent amount of it.
One last point to put the “Japan is a cash country” in perspective: In the USA you are typically limited to a daily withdrawal from the ATM of $300. In Japan the limit is roughly $5000. 
Oh well, lesson learned.