In Japan there are three main cellular service providers: au, Softbank (previously Vodafone), and (NTT) Docomo
When the iPhone first came out it was only released by Softbank, and later au and Docomo started carrying it. Mr. J and I use au as our mobile carrier, and when the iPhone 5 first came out my cellphone at the time was on its last leg, so I reserved one though them.
The iPhone 5 battery is infamous for dying after little use, and fast forward over two years later, mine was on its last leg. Like on the Kyoto trip my friends and I took, it would completely die after only taking 2-3 pictures or under 20 minutes of usage no matter if it was fully charged or not. So after the trip, I decided I needed to get the issue remedied ASAP before my next trip back to the States, and started the process of doing just that.