USD/JPY may indeed be headed for 120 like some would have us believe but that’s too ‘big picture’ for intraday traders and risk-reward would definitely seem to favour the intraday bears. 100.00 of course is a big psychological level and was an interim high back in April (see chart). It is also the 61.8% retracement of the move from 103.75 to 93.80.
Cheap and cheerful trades are always a good idea in my opinion, and selling near 99.90 with a tight stop above 100.40 looking for 98.00 looks like a reasonable strategy.