SoftBank Corp’s initial public offering today started with a bang before trailing off into a whimper, with the stock falling 14.5 percent during its first day of trading on the Tokyo Stock Exchange. The company is the mobile unit of conglomerate SoftBank Group, whose holdings also include Sprint and the $100 billion Vision Fund. Shares of SoftBank Corp opened at 1,463 yen, below the 1,500 yen the company had set for its IPO price (instead of a range), and closed at 1,282 yen.