You can see that USDJPY is engaged in an ascending channel pattern and this can last for a while before it breakdown. So, if you want to short, you got to be patient for this pattern to play out till the end. Any attempt to execute prematurely will not only tie up your capital but also affect your mood swing of seeing your paper profits turn loss turn profits, a volatile move. Unless you are able to capture the short term moves of up and down within the channel skilfully, I suggest being patient like a fisherman and wait out.