Each country has its own iTunes music store. In order to buy music in that country, you must set up a new Apple iTunes account, even if you already have an account in another country's music store.

Usually, the Japanese store requires one to have a Japanese credit card, but there is an alternative method of registration that allows one to register using only a gift card. That is the method I will describe here.

The Steps

1. Open iTunes and go to the iTunes Music Store.
2. At the bottom of the main page of the iTunes Music Store is a link to all of the different countries' stores. Click your current country, and then choose 日本 (Japan) from the menu.
3. You will be taken to the Japan Store. Click the "Redeem" link in the upper right corner of the page.
4. Enter your gift card code at the prompt. Click "Redeem."
5. A log-in window will appear. Choose "Create Account."
6. You will now need to enter some personal information to set up the account. Important: You must register an e-mail address that is not already registered with any iTunes accounts. You may need to make a new e-mail address with Gmail or Hotmail for this purpose.
7. Sometimes the next screen will allow you to choose "None" for your credit card. If so, skip this step. However, usually "None" is not an option the first time that you do this. In that case, you should click the "Home" link (the little picture of the house) at the top of the screen and start again. In most situations, "None" will appear the second time.
8. Once you have selected "None" as your credit, all that remains is to enter a Japanese address. The city, prefecture, and postal code must be valid; the addresses are not checked more than this, so it is possible to make up the rest, or use the address of a hotel or business.
9. Congratulations, your registration is complete! Enjoy the music!

Alternative Method

If you're having trouble with the steps above, particulary getting "None" to appear as a credit card option, try the following.

1. Go to the iTunes Japan Store. Navigate to the section with the iPod/iPhone apps.
2. Find a free app, and click "Get App."
3. Follow the steps from 4 on in the guide above. This time, "None" should appear on your first attempt.