Although USD/Yen has been trading in a relatively narrow range between 78.40 and 77.80 since mid-session Monday after Sunday evening's BOJ intervention (to sell yen and buy USD), all of the action off of the intervention high impresses me as a bullish digestion period ahead of another up-leg.
At this juncture, only a decline that breaks and sustains below 77.80 will morph the digestion pattern into something a bit less constructive. My sense is that the BOJ is under the market bidding for dollars beneath 78.00. The longer the BOJ contains new speculative selling pressure at or above 78.00, the greater the likelihood that USD/Yen shorts will "give up" on their positions for fear of getting caught in another painful round of BOJ intervention.
ETF traders may want to watch the ProShares UltraShort Yen (YCS).