Thanks for your suggestion. I think this should work, but unfortunately I don‘t have an actual address in Japan, so I would need to use a random address as you‘ve mentioned.
I‘m a bit hesitant to do this, because I have heard of cases where Amazon asked people with two addresses in different countries to prove that both are their actual addresses. So using a fake address to circumvent regional restrictions could even result in a closed account, I guess.
And then there‘s this story
of that Norwegian guy whose main amazon account has been shut down for unknown reasons because it was directly related to another account which has been previously closed for policy abuse.
So, when I create a fresh amazon account and a fresh JP amazon account (with fake data) and link them, amazon might shut down both accounts AND might even close my third main account when I use my credit card in all three accounts.
But maybe I‘m just overcautious...