Japanese men in their 30s and 40s are the biggest drivers of the bitcoin boom. 

Forty percent of bitcoin trading between October and November was conducted in yen, according to a Nikkei report.

Japanese investors, mostly men, came to dominate trading after regulators started to shut down cryptocurrency exchanges in China.

"More than a few Japanese investors positively value volatility," Muraki [of Deutsche Bank] said in a note on Thursday. He continued: "Japan’s investment style is typified by a combination of low-risk, low-return deposits and high-risk, high-return investments."

Many Japanese investors are engaged in leveraged trading, using borrowed funds. 

"We think that retail investors are shifting from leveraged FX trading to leveraged cryptocurrency trading," Muraki said. "Japan accounts for a high 54% of global foreign exchange margin trading (leveraged FX trading), so Japanese retail investors are major players in FX markets."