TOKYO, July 8 : Japanese asset managers, including the units of Mizuho and Nomura, are rushing to launch bond funds to meet soaring interest in Japanese debt as higher interest rates mean attractive yields for the first time in decades.The market is deepening as more Japanese firms issue bonds as a source of growth financing and Japan's asset managers are banking on their expertise in the corporate bond market to attract funds from investors slowly upping their allocation to yen-denominated debt.A yen bond fund established by the asset management arm of Mizuho Financial Group, Asset Management One (AMO), has secured its first mandate to manage funds on behalf of a Western institutional investor, two people familiar with the matter said.The people declined to be named as the deal has not be