Japan Inc. is already counting the cost of Brexit. The yen's extended surge after the United Kingdom voted to exit the EU has turned the outlook for a gain in annual profit to the first decline in four years.

Take Toyota Motor Corp., for instance.

Since the June 23 referendum, the mean forecast for net income at the world's biggest automaker has slid to $16.5 billion, with four analysts cutting their predictions by an average $2.3 billion for the fiscal year that started April 1. The referendum outcome triggered the yen's biggest one-day advance in almost 18 years, taking its gains against the dollar in 2016 to 17 percent, the best among developed nations.