The Premium Berry burger features a sauce made with raspberries, cranberries, blueberries, and red wine mixed with whole blueberries on top of bacon, a flame-grilled black pepper-mixed beef patty, lettuce, onions, and mayo. The burger might sound like a weird mix of savory and sweet but Wendy's offered a similar burger last year in Singapore (they called it the "Christmas Cranberry Burger"). The Burger King Japan version costs 590 yen (~$5 US).
The Mush 'N Cheese burger features a black pepper beef patty topped with a chopped blend of four mushrooms and a four-cheese sauce, plus a dusting of parmesan on a sesame seed bun. It goes for 480 yen (~$4.07 US).
Both burgers are available through December 25, 2014 (i.e. Christmas Day).
That's not all Burger King is offering for the Christmas season though: They're also selling Turkey Legs: