Dislikedhesitation ,Yen at 15 year low, Possible cautious in case intervention but as yet japan says "no comment".Ignored
http://fxtrade.oanda.com/analysis/fo...r-book#USD/JPY
and animate the open positions, you'll see that longs above the price have decreased in the last couple of hours, presumably because of the plummeting price their positions are getting closed. If the BoJ intervenes now, it would make a lot of those existing longs happy, but if they wait more and more of them will suffer and close their longs.
I really don't know why interventions don't first sell the currency, then re-buy (some or all) of it immediately causing a spike and hurting more.