Nikkei opened higher Monday on eased concern over Greece\'s debt problem. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 30.68 points, or 0.34 percent, from Friday to 8,977. 85. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was up 1.56 point, or 0.20 percent, at 780.63.