Kind of a quick digression from the rest of my trip report, but I just want to show you one thing that made our lives SO MUCH EASIER on this trip:
As is probably obvious, that's a Pocket Wifi LTE. It runs on Emobile's LTE network in Japan, which is extensive - they claim it covers 94% of the country. I got it from PuPuRu.
PuPuRu isn't really the cheapest or best known rental company, but they had the advantage of actually having this thing in stock at the last minute - a lot of rental companies sell out really early. Also, they have flexible rental periods; some companies charge you for either 7 or 14 days, but nothing in between. Pupuru just charges by the day, so the total price came out about average (about $10 a day). And the rental process was very easy - a package was waiting for me at my hotel, and returning it was as simple as dumping it in a mailbox right outside the security line at Narita Airport.
When I first went to Japan in 2000 and up to as recently as last year, I knew that as soon as I got on the plane at JFK, I was basically going to be in internet darkness for the most part until I got back. Even hotels there have spotty internet - at most, you're still lucky to get a wired connection for free. (An improvement over my first trip, when hotels there were still using dialup.) Forget about free public wifi, and a lot of American cell phones don't work in Japan. Mine does, but the roaming rates are ridiculous. I can't tell you how many times we'd get lost on every single trip to Japan - even people from Tokyo have trouble navigating the city because of its archaic addressing system.
Wifi is so bad there because domestic cell phone service is so good - that's what everybody uses when they're outside anywhere. So why not just carry a device that takes advantage of that? The Pocket Wifi is a mobile hotspot, and I was able to use it everywhere - even on trains, even underground, and in Okinawa too. It was awesome - especially now that Google Maps supports transit directions in Tokyo. We never got lost! And we had something to do during those long, boring subway trips.
I highly recommend this. One tip - get the one with the 7 hour battery, at least. And maybe rent a spare.
UPDATE: Went back to Japan about 8 months later and they gave us a newer model with a 12 hour battery. And it really did last that long - except for our very longest days, we had no problem just turning it on when we went out and leaving it on until we got back to the hotel at night. So the battery issues mentioned above may already be a thing of the past - but you might want to ask when you pick it up if you're getting the 12 hour model.