TOKYO (Reuters) - Japan's SoftBank Group&nbsp;Corp on Wednesday said it has agreed to buy Fortress Investment Group&nbsp;LLC for about $3.3 billion, looking to add investment expertise as it prepares to launch the world's largest private equity fund.<div><a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=itLdrTnsGIk:fd4QZJHAU0I:yIl2AUoC8zA"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?d=yIl2AUoC8zA" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=itLdrTnsGIk:fd4QZJHAU0I:V_sGLiPBpWU"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=itLdrTnsGIk:fd4QZJHAU0I:V_sGLiPBpWU" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=itLdrTnsGIk:fd4QZJHAU0I:-BTjWOF_DHI"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=itLdrTnsGIk:fd4QZJHAU0I:-BTjWOF_DHI" border="0" /></a></div><img src="http://feeds.feedburner.com/~r/reuters/technologyNews/~4/itLdrTnsGIk" height="1" width="1" alt="" />