Take your pick; more talk on the Council for Economic and Fiscal Policy (CEFP) will meet soon to promote more aggressive easing and other policies to stimulate the economy; also BBC reports that North Korea plans more long-range missile tests.
Probably a combination of the two, along with short covering after the Chinese PMI, are the likely reasons behind the rise in USD/JPY.
Stay in range trading mood is my view, and use rallies as selling opportunities.