How much does it cost for Japanese tourist duty-free shops to be tax-free?

There is no requirement for the amount. In Japanese duty-free shops, you can show your passport and air ticket and buy duty-free goods directly.

Duty-free shops in every country have different shopping methods. For example, when shopping in a duty-free shop in Korea, you must provide a passport and a return ticket. If you buy something, you can take it away if it is a Korean brand, but you can't take it away if it is a foreign brand. You must pick it up at the airport when you come back. There is a limit to the quantity. In Japan, you can show your passport and air ticket and buy duty-free goods directly. Duty-free shops in Hong Kong are actually fake, because Hong Kong itself is a free port, with no tariffs and no formalities. Any store in Europe can buy goods and then refund the tax at the airport with the invoice. Only international airports in the United States have duty-free shops, which can be picked up at the boarding gate after purchase.