Maggie is smarter than the iTunes Music Store
So iTunes won't let you buy from iTunes Japan with your American iTunes store account. If you try to make an iTunes Japan account, it won't let you unless you have a credit card with a billing address in Japan.
Even if you happen to have bought an iTunes gift card in Japan, you cannot apply it to your American iTunes account nor can you open a Japanese iTunes account without providing a Japanese address, nor can you open a Japanese iTunes account with the same email you used to create your American iTunes account. It also tries to redirect you to the American iTunes store before giving you a chance to enter your Japanese address. HOWEVER. If you have a Japanese iTunes gift card, and open a new iTunes account with a Japanese address (and using an email address not associated with your American iTunes account), but do not enter a credit card for that account, iTunes Japan will allow you to redeem your Japanese iTunes gift card with no further hoops to jump through.
Maggie: 1
iTunes: 0
Even if you happen to have bought an iTunes gift card in Japan, you cannot apply it to your American iTunes account nor can you open a Japanese iTunes account without providing a Japanese address, nor can you open a Japanese iTunes account with the same email you used to create your American iTunes account. It also tries to redirect you to the American iTunes store before giving you a chance to enter your Japanese address. HOWEVER. If you have a Japanese iTunes gift card, and open a new iTunes account with a Japanese address (and using an email address not associated with your American iTunes account), but do not enter a credit card for that account, iTunes Japan will allow you to redeem your Japanese iTunes gift card with no further hoops to jump through.
Maggie: 1
iTunes: 0