A Tokyo firm is pinning hopes that the aging of wine at an undersea cellar off Amami-Oshima Island in Kagoshima Prefecture, southwestern Japan, will help revive the local economy. Underwater aging of wine is a widely held practice around the world, as submerged conditions — consistent and relatively cool temperatures, higher pressure and the absence of excessive light — are suitable for wine to gracefully mature. But the process is “rarely practiced in Japan,” said Yui Moritani, the 38-year-old president of a public relations firm in Tokyo that began the project. In late January, about 500 b…