The recent bullish price action in USD/JPY has been caused by the BOJ's announcement that they will continue their QE program indefinitely. This combined with the FED ending theirs, makes upside plays the only option in USD/JPY.
The monthly chart below highlights the break of a very important trend/channel line.
(Note the gold line on the monthly. I've highlighted an instance where a short position is safer. Price was still in a downtrend and struggled at the 120 level. Once back under the 50 ma, it stayed there for 5 years on a monthly basis).
The fundamental and technical picture make this a long only play for now. I would only buy on pullbacks however, by reverting to the weekly chart for entry.