JPY is one of the favourable funding currency (people short yen while long other currencies). during crisis, people tend to have the risk aversion mind-set. so they start to unwind the trade. as more people unwind the trade, the yen is being bought more and more, the price goes up; while many hedge funds and institutions have their stop-loss triggered during the yen appreciation, and the whole situation become worse. that is why we see a huge rise in yen crosses.