change Japan store to Untied states

All iTunes accounts are free. You are currently in the US (you have to be in a country to use its store) ? After entering your US payment details you should be able to remove them : Why can’t I select None when I edit my Apple ID payment information? - Apple Support

If you changed your country or region

When you change the country or region of an existing Apple ID, you must provide a payment method and update your billing options. If you want to remove your payment method after you change the country or region, you can change your payment information to None.

When you move country you are likely to be asked for card details (which you should be able to remove after entering) : Why can’t I select None when I edit my Apple ID payment information? - Apple Support

When you change the country or region of an existing Apple ID, you must provide a payment method and update your billing options. If you want to remove your payment method after you change the country or region, you can change your payment information to None.

If you don't have a valid payment method for your new country then you could try contacting iTunes Support and see if they can stop the requirement appearing : https://www.apple.com/emea/support/itunes/contact.html

You've read my above reply about why 'none' isn't there ?

When you change the country or region of an existing Apple ID, you must provide a payment method and update your billing options. If you want to remove your payment method after you change the country or region, you can change your payment information to None.