The BOJ (Bank of Japan) will release their monetary policy statement and the economic outlook report tomorrow morning at around 1 am GMT. A few hours later they will hold a press conference. This whole two week period leading to this meeting has been a bit of a melodrama. At first, there were rumours of a combined fiscal and monetary 20-30 trillion Yen stimulus package. 

Then the Japanese Prime Minister Abe and the head of BOJ Kuroda met with former FED chairman Bernanke and everyone assumed that the Japanese would start a helicopter money programme. That sent the Yen falling hard and USD/JPY surging more than 700 pips. But, Kuroda appeared again and he denied such a programme. 

Then, someone heard a whisper somewhere that the stimulus package would be around 6 trillion Yen and USD/JPY immediately fell more than 250 pips. Kuroda had to reappear and again deny such rumours, saying that the stimulus package would be around 28 trillion Yen. The BOJ is forced to act because the market is holding a gun to its head. 

If they don´t USD/JPY would quickly tumble below 100. I believe they will deliver what have promised tomorrow, the problem is how much of it is already priced in. The forex market is expecting a 28 trillion stimulus package so it won´t be a surprise. The BOJ has to support it with dovish comments for more monetary and fiscal easing in the months to come in order to have an impact. Who would want to be a central banker, eh?