There's no clear explanation for the price action in North American trade today in USD/JPY. You can see what happened here:
USDJPY 10 min
The rally might have gotten some added juice from stops as the February and 2023 high of 135.23 broke.
However it's since reversed in a big way despite no much change in the mood in equities. One driver is likely bonds as a decent bid comes through for 10s on the rejection of 4%. There's also a strong bid in European bonds -- particularly in Italy -- that could be helping the yen bid more broadly as differentials narrow.
There were also more comments from Kuroda about continuing easing. That's a boilerplate statement at this point and, if anything, it would contribute to yen strength not the weakness we're seeing.