* Bernanke remarks sees yen at 103 to dollar, aids exporters * Nikkei heads for fifth straight day of gain * Fast Retailing jumps as retail investors in hot pursuit By Dominic Lau TOKYO, May 23 (Reuters) - Japan's Nikkei average soared 1.9 percent to a 5-1/2-year high on Thursday, aided by exporters as the yen weakened against the dollar after the U.S. Federal Reserve chief suggested the central bank could scale back stimulus in coming months. The Nikkei <.included Honda Motor Co, Canon Inc , TDK N225> was up 303.11 points to 15,930.37 after trading as high as 15,942.60, its best mark since December 2007. The index was heading for a fifth straight day of gain. "The focus today is that the yen pushed to 103 last night on the back of comments out of the U.S.," said Stefan Worrall, director of equity cash sales at Credit Suisse in Tokyo. "It's going to be a huge fillip for the market. Any weakening of the yen would be. Also, it's evident of the strength of retail investors and their optimism." Bernanke told Congress that a decision to taper the $85 billion in bonds the Fed is buying each month could come at one of the central bank's "next few meetings" if the economy looked set to maintain momentum. His comments lifted the dollar to a fresh 4-1/2-year high of 103.74 yen on Wednesday. The Japanese currency was last traded at 103.48 on Thursday. Exporters on the rise Corp and Ricoh Ltd, up between 2.9 and 6 percent. But Mitsubishi Motors Corp lost 6.7 percent after sources said the automaker is considering wiping out about 920 billion yen in accumulated loses by reducing capital stock by an equivalent amount. Such a move is a common step for Japanese firms with a history of deep losses that have returned to profitability and want to begin paying dividends. The broader Topix added 0.9 percent to 1,287.26. Index heavyweight Fast Retailing Co Ltd jumped 5.1 percent, extending a 7.4 percent surge in the previous session as retail investors were in hot pursuit of the operator of casual fashion chain Uniqlo. It was the top-weighted gainer in the Nikkei. "Retail investors are very active in this market. They are using Fast Retailing as a home camp," a Tokyo-based trader said. "It's an indicator of the extent of the retail investors' involvement in this market." Interest from foreign investors was also high, with government data showing they bought 716 billion yen ($6.9 billion) worth of Japanese equities last week. They have ploughed a total of 8.28 trillion yen into Japanese stocks since the end of 2012. The benchmark Nikkei is up 14.8 percent so far this month, on track for a 10th straight monthly gain - its longest such winning streak since 1972. The index has rallied 53 percent this year, supported by aggressive government and central bank policies to revive growth, and it has risen 12 percent since May 9, when the dollar broke above the 100-yen mark. "We cannot rule out the chance of the Nikkei climbing to the 18,000 level if the dollar/yen continues to test 110 or 120 (yen). However, investors may consider taking profit as the rally is substantially running ahead of the fundamentals," BNP Paribas wrote in a note. It recommended investors buy Nikkei December call spread in case the index moves higher.