Please leave Japan within 90 days, counting from the day after your purchase, and complete customs confirmation before you check your baggage.
Complete it at the international airport or seaport from which you finally leave Japan. If you first take a domestic flight in Japan and then transfer to an international flight, complete the confirmation at the airport from which you finally leave Japan. If you have a connecting flight or your baggage is checked through, please check with your departure airport for how to proceed, or refer to Japan Customs' guidance (Japan Customs: Locations of Tax Refund Kiosks and Customs Inspection Areas). Customs makes the final decision.
Using a Tax Refund Kiosk or having your items inspected by a customs officer can take a while, so please allow plenty of time.