SoftBank's ascent to becoming Japan's most valuable company has put the spotlight on the conglomerate, raising questions whether it is taking on too much risk through its highly leveraged bet on artificial intelligence. Shares of the Japanese technology investment giant, led by founder Masayoshi Son, have surged about 70% this year on investor enthusiasm over AI, buoyed by the soaring valuation of chip designer Arm Holdings and expectations that OpenAI could see a blockbuster initial public