I thought I'd post this here since a couple of others have indicated they're also going to Japan next year for the first time. For those of you who may want internet connectivity without hefty roaming charges. Public wifi is virtually non-existent for tourists in Japan, and still many hotels don't have free wifi. I hired a portable wifi unit, there's a few companies offer them, but the best I found was eConnect as there were no hidden charges. Some companies charge extra for a charger, extra admin fees etc! eConnect just charged me one price and the equipment was delivered to my first hotel, already charged, with a charger and a carry case. As an example of cost I paid just over 9000 Yen / approx. £55 for 12 days, unlimited data and all I had to do was put it in a prepaid envelope and post it on my way to the airport on the last day.
So if you're interested the website is:
http://www.econnectjapan.comYou can connect usually up to 5 devices over secure wifi, service is good and we had no problems. I like to use internet whilst I'm out and about, not just in my hotel room, for things like mapping, transport routing, restaurants etc.
Hope that's useful to some of you.