A two-day drop in SoftBank Group Corp. shares has resulted in a $2.5 billion loss for its founder, Masayoshi Son, following an unexpected interest-rate hike by the Bank of Japan. The company’s shares fell 6.7% in morning trading in Tokyo, marking a roughly 13% decline over two days. Despite this setback, Son’s fortune remains up by about $3 billion from the $11.3 billion he started with at the beginning of the year, according to the Bloomberg Billionaires Index.