NEW YORK (Dec 15): It’s not drug dealers and tax cheats, it’s Mrs. Watanabe.

That term is often used to describe the individual Japanese investor, traditionally a housewife who runs her family’s finances. And that’s who behind the surge in bitcoin, according to a Deutsche Bank AG note Thursday.

“We think that retail investors are shifting from leveraged foreign-exchange trading to leveraged cryptocurrency trading,” analysts led by Masao Muraki wrote.

Japan accounts for about 50 percent of global foreign-exchange margin trading, according to Deutsche Bank. The bank pointed to a Nikkei report saying that about 40 percent of cryptocurrency trading was yen-denominated in the October and November and is likely rising since China started to shut down digital-currency exchanges.

But it might be more apt to pin the surge on Mr. Watanabe, since Japanese men hold 79 percent of foreign-exchange trading accounts, Deutsche Bank said. And 63 percent of these are aged 30-49.

The retail-investor led surge in interest for bitcoin may not end well if prices begin to decline in the wake of this year’s more than 16-fold surge, the bank said.

“The risk of incurring losses greater than margin is higher than in normal foreign-exchange trading, due to high intraday volatility,” the report said. “Furthermore, as speculation in cryptocurrency is growing to a scale that cannot be ignored, we plan to look more deeply into the potential impact on the market if the bubble should burst and the effect of concerns over this on regulations and monetary policy.”

The Watanabes could be facing some marital discord.