What has dropped the yen to the worst levels since May

Bloomberg lays out eight factors:

  1. Dollar demand seen from global central banks especially in 2-year and 5-year notes
  2. Japanese moves ahead of year end
  3. Short covering and a run on stops
  4. A surge in yen options trading on the break of 110.00 and related to coronavirus fears
  5. An unwind of shorts in USD/JPY and EUR/JPY
  6. Chinese measure to support parts of its economy reduced safe-haven demand
  7. Technical momentum
  8. Worries about a recession in Japan

Many of these overlap but that's the buzz.