Article in the Wall Street Journal:

Yen's Resilience Causes Investors to Shift Bets
Money managers slash wagers against Japanese currency

May be gated, but in brief:

One of Wall Street's favorite pastimes, betting against the Japanese yen, has lost its zing this year.

In a year characterized by wild swings in major currencies, including a one-day, 41% surge in the Swiss franc against the euro, the yen has risen against the euro and largely held steady against the dollar.

More:

The yen's strength stems from several factors. BOJ officials face constraints in boosting bond purchases, including the bank's already large presence in the bond market.

And many politicians have come to conclude that further yen weakness would do more harm than good, by lifting import prices for consumers and small companies.

Meanwhile, USD/JPY has had a little jump in early Tokyo: