TOKYO—One of Japan’s biggest stock investors just reported record gains of more than $50 billion after a well-timed bet. But the person who engineered the windfall won’t be getting a Wall Street-style bonus this holiday season, and some have even started saying he shouldn’t play the market so much.
That’s because the hot-hitting portfolio manager is Gov. Haruhiko Kuroda, head of Japan’s central bank. Mr. Kuroda has led the Bank of Japan’s push, unusual among global central banks, to invest in the Tokyo stock market as a way…
