Burger King Japan brings back the Mushroom Whopper on Friday, September 18, 2026, in three sizes — regular, Double and Jr. Each one stacks four mushrooms (two roasted varieties plus eringi and bunashimeji) over a flame-grilled 100% beef patty, finished with a Premium Pepper Mayo Sauce. An app-only coupon runs through October 1, cutting 300 yen off the regular and Double sets, up to 23% off. An Autumn Icon Returns for a Limited Time BK Japan Co., Ltd. (headquarters: Chiyoda-ku, Tokyo; President & CEO Kazuhiro Nomura), operator of Burger King® in Japan, will bring back its beloved autumn classic, the Mushroom Whopper® line-up, from Friday, September 18, 2026, for a limited time. Three items are available: the Mushroom Whopper®, the Double Mushroom Whopper®, and the Mushroom Whopper® Jr. For many fans, this burger has become the signal that autumn has truly arrived. Four Kinds of Mushrooms and a