After correctly predicting its advance beyond ¥115 and then ¥110 per dollar, Eisuke Sakakibara now says the nation's currency may strengthen to ¥100 by year-end.

The former Finance Ministry official in charge of currency intervention, who was dubbed Mr. Yen for his ability to influence the exchange rate in the 1990s, said it may advance to ¥105 in the next few months. The currency has surprised analysts this year, surging from around ¥120 per dollar to reach ¥107.63 Monday, the strongest since before the central bank expanded its quantitative easing program in October 2014.

The yen has renewed its highs despite increased rhetoric from Japanese officials in the past week aimed at restraining its advance. Bank of Japan Gov. Haruhiko Kuroda said Monday financial markets continue to be volatile, and he is watching the effect on the economy.