The BOJ is going to be messy one way or another but there is only three things you need to watch

I've been thinking about the possible moves tonight and it I can sum them up in three points

  1. The BOJ don't do anything - Yen pairs fall hard.

  2. They act - Yen pairs rally as soon as the headlines hit. The market won't read the details in the first couple of minutes, it will be buy first, ask questions later.

  3. The market reads the small print - After the initial reaction, the market will look into the details and decipher what they mean. This will either cause yen pairs to rise further or fall if the market is disappointed

Use these three points as a guide to any trades you are in as they could save you from getting whipped about. If you are long yen pairs into the decision and you get that initial jump, I'd suggest thinking about locking in or taking some off quickly so that you don't give it all back if the market goes against you on part 3.

For no action, the trade is pretty clear.