Japan's central bank recently instituted a significant expansionary monetary policy. The market's immediate response was to increase, and the rise has continued since the announcement. Easy money provides liquidity. While this can be offset by inflation, the lack of wage growth has kept inflation muted. Thus, equity markets have responded favorably. See article here, The Economist.
Dolvin, Steven D., "Central Banks Propel Equity Markets" (2013). All Chapters. 70.