When the nukes shut down Japan started imported a lot more oil etc. And their trade surplus started fading and yen became ‘easier to get’ internationally.

Meanwhile, conditional funding in the euro zone worked to take away the euro evaporation risk, while the austerity continued to make the euro ‘harder to get’.

And the US cliff is making the dollar ‘harder to get’ and about to get more so.

And Japan’s fx reserves keep marching higher indicating that somehow yen are being exchanged for dollars that Japan keeps at the Fed, and probably same with euro, as the euro zone has been encouraging foreign buying of euro. All making euro and dollars ‘harder to get’

The Fed’s growing portfolio continues to remove interest income from the global economy, making the dollar ‘harder to get’.

So if nothing else changes the yen goes down until net exports rise sufficiently.

Just like the euro goes up until that trade surplus goes away (or the euro zone goes away, which ever comes first, but that’s another story), and the dollar keeps fundamentally firming until fiscal relaxes.

Regarding the yen, however, a falling yen doesn’t necessarily cause trade to reverse. In fact, initially, the rising price of oil, for example, exacerbates the fall, as the quantity purchased doesn’t immediately fall. Nor does the drop in real wages immediately cause exports to rise.
This was called the J curve when I was in school back in the last century.

And not to forget Japan thinks a falling yen is a good thing.

So given all that, the J part could go a lot further than markets currently are discounting.