Customers of Amazon.co.jp will need to create a new account on Amazon.comFuck off Japan. No, just fuck off. There is always something in Japan's import or content laws to fuck up things for the consumer, and much like how they build, belies it as a 'First World' country.
I bought the Kindle hardware via Amazon Japan, and I checked I could reregister the location to Canada/USA later, as I am leaving in over a year, and because I assumed there would be reduced content on Amazon Japan. The content is fine, but that the app doesn't link to Amazon Japan, but seems to in other countries is the usual Japan BS. I don't even know why, or care, but can guarantee it is on the Japanese end. (Canada's Kindle seems to link to the US, which is fine). So I was wrong about why I would need to be able to deregister the Paperwhite and my account from Japan, but I was right that I would need to, long before leaving Japan.
What one does, and I will do, is link the Japanese Kindle account with the ebooks one has bought on Amazon Japan to a US account, or Canadian one (just make sure your account has an in-country address or you may have trouble), and move the Kindle registration to the same US or Canadian Amazon account. I have an account in all three countries... Because hey, maybe I want to be able to have my ebooks at both my reading devices, and even my laptop, all on the same account and equally accessible to each device!
Fuck off Japan.
And I still have not figured out how to get my Docomo Galaxy 3 to tether to my Paperwhite!
To answer kathrynoh's comment, "Why not just one Amazon?", much of it must be about licences and taxation. And I do not know if Amazon Canada or Japan has fewer English ebooks, but I do know that the US site has them all, but not Japanese titles. Still, seems like there should be one damned site at which you could choose your location and language, and Amazon sort out the licensing and shipping efficiency. Maybe the way to go is to use your local Amazon site for anything physical, but the US site for anything digital. You need an American address to avoid trouble, but surely everyone has a friend in the US... Do not know how much trouble you might have if you do not have a US credit card for buying ebooks. I have ordered gift certificate to relatives in the US, and physical objects sent to a friend's address in the US, all on Canadian and Japanese cards: no ebooks yet.
I am trying to convince the J-wife she needs an Android tablet so she can get her own Japanese books in Japan and in Canada, and for the hybrids. She'd need to use the Japanese site, of course. kathrynoh, have you tried putting in a fake Japanese shipping address? For media it's not like anything will physically ship...