Tokyo stocks opened 0.31 percent lower on Wednesday after a warning over foreign exchange volatility from the Group of Seven richest nations pushed up the yen.
The Nikkei 225 index at the Tokyo Stock Exchange was down 35.40 points to 11,333.72 at the start.
The yen climbed after the G7 said on Tuesday that "excessive volatility" in exchange markets hurts financial stability in a move to calm talk of currency wars before this week's G20 talks in Moscow.
Japan's policy of monetary easing has stoked fears, especially in Europe, of a so-called "currency war" between the major economies in which policymakers seek to devalue their currencies to make exports more competitive.
"The yen may be on the agenda at the G20," warned Hideyuki Ishiguro, senior strategist at Okasan Securities.
"Stocks are likely to face selling for now," he told Dow Jones Newswires.
In early Asian trade on Wednesday it took 93.27 yen to buy a dollar and 125.48 yen to buy a euro, stronger than 93.47 yen and 125.75 yen in New York Tuesday afternoon.
The Japanese currency was much weaker on Tuesday morning, with the dollar trading above 94 yen and the euro above 126 yen.
The euro bought $1.3452 Wednesday morning, almost flat from US trade.