The Pasmo/Suica cards are intriguing, they are NFC, but also store the last few transactions on the card itself, there are also mobile apps for scanning these cards to see how much credit you have left and list the above-mentioned transactions.
My Japanese feature phone back in 2009 could also use Mobile Suica with a dead battery. I believe at the time the NFC wasn't active like on the iPhone but a passive "card" that was reprogrammed by the phone and didn't need power.
The iPhone only got this "power reserve" recently.
I’m a huge fan of the Pasmo/Suica cards. They’re easy to obtain and easy to accept payments, so uptake is huge (if memory serves me correctly, literally accepted everywhere?). You get most of the benefits of card payments (fast, no fiddling with change, no “do you have a smaller note”), but you also maintain anonymity which is a common argument I hear against cards in Germany and why card payments are so rare there (at least in 2017, I don’t know if the situation has changed).
Something like that (for general payments, not for public transport) used to exist in Germany ("Geldkarte"), but it never became a big success and is now being discontinued. And personally speaking – not being able to easily look up how much money is stored on that card is somewhat annoying, so I'd rather continue carrying cash in that case.
They’re not quit accepted everywhere. Mostly in high convenience, small purchase places. You can get multiples of them for maximum privacy, but they’re 500yen each to purchase.
It was a feature all along since flip phones implementation, which was replicated and one-upped on iPhone. Phone implementations run from leftover charges on empty battery, not by power from the reader(which requires a coil).
