People used to talk about a "Greenspan Put." The idea was that if the markets fell too much, Greenspan, then the chairman of the Federal Reserve, would step in and prevent investors from losing too much money. The effect was almost as if they had bought an option - a put - to protect themselves from a large drop in the markets.
These days, it is looking like there is a BOJ/MoF put for people interested in selling the yen. Selling the currency with the lowest interest rates, which in recent history has been the yen, is a popular trade because if markets don't move then the seller will make money*.
Recently, the yen has actually been strengthening, but Japan's finance minister just announced that they were buying dollars and selling yen when the yen was trading around 83. The Bank of Japan released a statement supporting these actions.
The Bank of Japan strongly expects that the action taken by the Ministry of Finance in the foreign exchange market will contribute to a stable foreign exchange rate formation.
Traders interested in selling the yen and buying the dollar are able to take large positions when they believe they have a central bank backstopping their trade. Of course, this backstop only matters when the traders selling yen have been losing money, so the best way to trade it may be from a tactical perspective of fading yen rallies rather than a long term "sell and hold" approach.
*Short term interest rates in the US are low enough that this isn't as profitable to do versus the dollar unless a longer term currency forward is used. If a longer term forward contract is traded, the trade is impacted by both movements in interest rates and in currencies. This isn't as popular as trading purely currency or purely interest rates because most traders like to take specific risks and avoid exposure to variables that they are less familiar with.