I'm no expert, nor do I play one on TV. However, at least one of the greatest export competitors to the Japanese is the Chinese. As was pointed out, the Chinese Yuan is tied to the US dollar. If the US dollar falls against the Yen, or the Euro, or the Australian dollar, the Chinese Yuan falls by the same amount. The US dollar was falling against the Yen, and the Japanese exporters were screaming bloody murder, so the BoJ purchased huge amounts of US government debt to prop up the dollar's value, at least vis-a-vis the Yen, to reduce the Yen's strengthening against the Yuan. My 2 cents.