This has just happened this morning:
http://finance.yahoo.com/news/Japan-intervenes-in-currency-apf-162919431.html
Japan intervenes in currency market to weaken yen
TOKYO (AP) -- Japan waded into the currency market Wednesday for the first time in six years, buying dollars to weaken the surging yen, which is battering famed Japanese manufacturers like Toyota and Sony after spiking to 15-year highs.
...
The currency has risen about 10 percent against the dollar this year, and business leaders had been pressing the government for help. A strong yen hurts exporters -- the mainstay drivers of the country's still-fragile economic recovery. It erodes their foreign income when repatriated and makes their products less competitive in overseas markets. Toyota Motor Corp. estimates that every 1-yen climb versus the dollar saps 30 billion yen ($351 million) from earnings.
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The yen, meanwhile, is seen as a safe haven currency. Japan's government debt is largely owned by domestic investors, making the country less at risk to the capital flight that can occur when economic or political shocks cause confidence to collapse.
And even with interest rates near zero, Japan's real interest rate is higher because of persistent deflation. For foreigners, that means yen-denominated assets will look more attractive as prices keep falling.
