During Monday's trading session, the Japanese Yen appreciated 54 pips or 0.50% against the US Dollar. Note, that the US Dollar also depreciated significantly against gold.
The reason for the advance was the announcement from the Chinese government that it would impose tarrifs on $60B of the US goods from June 1.
Most likely, the demand for the Japanese Yen and for gold has increased as for the safe-haven assets.