Usually after 5 books, it seems like most people who don't use VPNs have problems.
To use a VPN, first you need to find a VPN service provider who has a server in Japan. (I use TorGuard, and they have Japanese servers, along with a bunch of others. You only need the VPN service, you don't need their BitTorrent service, unless you want it.)
Sign up for the service, then follow the instructions for the device of your choice. The instructions vary depending on whether you're using a computer or a tablet/phone. (Don't use the Paperwhite.) You could set up your router to use the VPN service, I suppose, but some VPNs may not support that. It also depends on your router firmware. I know DD-WRT supports it. The downside is that ALL of your internet traffic will get funneled through the VPN, and everything will slow to a crawl. VPNs are slow.
Essentially, you want to set up a machine to access the VPN, and use it to buy the content. Amazon or whoever will see your IP, and think, "Oh, that's in Japan. Approved!" and okay your purchase. Then you can download it from your Paperwhite without the VPN if you want. (Because you've already purchased it.)
Tin Foil Hat Route: Now, if you *really* want to be paranoid about it, put your Paperwhite in Airplane mode, and leave it there when you use it. Only take it out of Airplane mode to download books. And only download books a day or so after buying them. (In case someone wrote a smart little program to check for instantaneous downloads from a foreign IP!) But like I said, that's the paranoid route.
Also, none of this guaranteed to work, and it's subject to change at the drop of a hat. Welcome to the world of mass media controlled by clueless megacorporations. It's been 8-9 years or so since eInk eBooks became a Thing, and they still don't know how to stop tripping over their own feet. *sigh*
To use a VPN, first you need to find a VPN service provider who has a server in Japan. (I use TorGuard, and they have Japanese servers, along with a bunch of others. You only need the VPN service, you don't need their BitTorrent service, unless you want it.)
Sign up for the service, then follow the instructions for the device of your choice. The instructions vary depending on whether you're using a computer or a tablet/phone. (Don't use the Paperwhite.) You could set up your router to use the VPN service, I suppose, but some VPNs may not support that. It also depends on your router firmware. I know DD-WRT supports it. The downside is that ALL of your internet traffic will get funneled through the VPN, and everything will slow to a crawl. VPNs are slow.
Essentially, you want to set up a machine to access the VPN, and use it to buy the content. Amazon or whoever will see your IP, and think, "Oh, that's in Japan. Approved!" and okay your purchase. Then you can download it from your Paperwhite without the VPN if you want. (Because you've already purchased it.)
Tin Foil Hat Route: Now, if you *really* want to be paranoid about it, put your Paperwhite in Airplane mode, and leave it there when you use it. Only take it out of Airplane mode to download books. And only download books a day or so after buying them. (In case someone wrote a smart little program to check for instantaneous downloads from a foreign IP!) But like I said, that's the paranoid route.
Also, none of this guaranteed to work, and it's subject to change at the drop of a hat. Welcome to the world of mass media controlled by clueless megacorporations. It's been 8-9 years or so since eInk eBooks became a Thing, and they still don't know how to stop tripping over their own feet. *sigh*