supaginge If you buy at a store that supports tax-free shopping for foreigners, then basically just mention tax-free when purchasing. You need to show passport, and they should know what to do from there. Then you just have to pay item price without consumption tax (10%). If you want to know all the details have a look here, depending on how much shopping you plan on doing in Japan it can save you a lot of money.
In theory, if you use "Visit Japan Web" app for immigration procedure you can also get a special QR code for tax-free check out that is supposed to work without showing your passport, but in real world you always need your passport. "Visit Japan Web" is still useful just for going through immigration and customs quickly, I recommend using it.
Of course, Amazon or other web shops (check Kakaku maybe) might still be cheaper even without the tax rebate. Have a good trip. Maybe if Google releases the 9a soon-ish then I can switch devices and try FeliCa usage with the new one.