Nikkei opened at a fresh 21-month high in early trading Friday, the last session for 2012, as the yen weakened further amid expectations of bold monetary easing in Japan. At 9:15 a.m., the 225-issue Nikkei Stock Average was up 75.21 points, or 0.73 percent, at 10,398.19, its highest level since March 10, 2011. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was up 3.70 points, or 0.43 percent, at 857. 79.