TOKYO, Dec 17 (Reuters) - Japanese shares closed higher for a second straight session on Thursday as expectations for further U.S. economic stimulus and a pledge of support from the Federal Reserve lifted sentiment. The Nikkei 225 Index closed up 0.18% at 26,806.67, reversing losses from morning trade. The broader Topix rose 0.32% to 1,792.58. Some traders were slightly cautious as Japan grapples with a third wave of infections, but positive developments in the United States offered support. Top Democrats and Republicans sounded hopeful about agreeing on a $900 billion COVID-19 aid bill, and the Fed vowed to keep pouring cash into financial markets until its economy is on a sound footing. Stocks could easily fall on profit-taking after the Nikkei hit a 29-1/2-year high last week, but analysts have an upbeat mid-term outlook. “Excessive amounts of liquidity provided by central banks have been the backbone of stock markets this year, and this will continue into next year,” said Norihiro Fujito, chief investment strategist at Mitsubishi UFJ Morgan Stanley Securities. Top gainers among the top 30 core Topix names were Nintendo Co Ltd, up 6.61 %, followed by Keyence Corp, up 5.3%. The underperformers were Daiichi Sankyo Co, down 4.40%, followed by Central Japan Railway Co, losing 2.23%. Japan Post Insurance rose 10.05% on media reports that it would buy back $2.9 billion of its own shares from its parent Japan Post Holdings, whose shares rose 3.58%. Fujifilm Holdings fell 3.0% after a media report said that Japan’s government concluded it could not measure the effectiveness of the company’s Avigan drug as a treatment for COVID-19. There were 56 advancers on the Nikkei index against 166 decliners . The volume of shares traded on the Tokyo Stock Exchange’s main board was 0.98 billion, compared with the average of 1.35 billion in the past 30 days. (Reporting by Stanley White; Editing by Aditya Soni and Uttaresh.V)