@Spotspot01 Sorry for the late reply, a combination of work, procrastination, and mild sickness kinda kept me from logging onto MangaDex or working on translation/scanlation for the past couple weeks.
As far as buying Japanese Kindle books, you do not need to use a VPN or change your currency. Just register a new account on
https://www.amazon.co.jp/. It's best to use an email that's different from the one you use for your domestic Amazon account if you have one. It'll work if you use the same email but Kindle might get confused when you log into it (e.g. showing you the wrong account). If you do prefer to use your same email, just make sure the password is different from your other Amazon account, and it'll be fine 99% of the time, I think.
Here's
a guide that pretty much covers the entire process. It's a few years old, but I don't think much has changed and it should still be accurate. Basically you'll be getting an address from a forwarding service and using that as your address for your account. Since your purchases will all be digital, you won't need to worry about anything being shipped there. Of course, use your proper billing address when adding credit/debit cards.
In regard to credit cards and currency, since it's Amazon, they take almost any card from most countries. At the very least, all of my US cards work. You shouldn't have to change your currency yourself, your card company should do that for you. They'll tack on a small fee (usually called a foreign transaction or currency conversion fee) for doing so, usually 1-3%. I should also note that since it's a foreign purchase, your card company might flag it as identity theft or something and deny the purchase, in which case you'll have to call them to straighten it out.
By the way, the poster of the guide I linked to above has a note at the bottom saying they were cut off after a certain number of purchases. This led me to check my own number of purchases, and I'm at about a thousand on Kindle, so I'm not sure if I'm lucky or the poster was unlucky or the limit is pretty high or what. I make virtually all my purchases through the Kindle app on my android phone, but I don't think that should matter since I don't use a VPN on my phone either. Anyway, just something for you to consider.
This became a rather long reply, hope you can be bothered to read it all xD. And thanks for the compliment on my scanlations!