Adds some clarification
The USD/JPY options market is said to be short of topside gamma, which means it doesn't have an awful lot of existing options coverage to the topside.
Big stops lurk in the mid 109s and any break there can increase volatility because of the lack of options and related hedging flows in the spot market.
USD/JPY implied vols are cheap after months of low realised volatility, so they are likely to rise if spot breaks higher, especially if spot volatility increases.
Consider an out-the-money JPY put option with a short-dated expiry.
It's cheap, but would benefit from increased volatility, as well as capturing the gains in spot.
With spot at 109.10, a one-week expiry, 109.50 strike JPY put has implied volatility of 4.5 and costs 11 pips in premium (the total amount risked).
Even a rise to 109.50 and a 0.5 gain in implied vol would more than tripple the initial out-lay.
There are already similar strategies trading -- size buyer two-week 110.00 earlier nL2N27N071 .
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