SoftBank Group Corp. experienced its largest single-day stock decline since going public in 1998, with shares plummeting 19% and wiping out $15 billion in market value amid a global sell-off. This downturn has significantly impacted founder Masayoshi Son, whose net worth dropped by approximately $4.6 billion in one day. The decline is attributed to rising interest rates from the Bank of Japan, a strong yen, and broader concerns about a deteriorating economic outlook in the U.S. Analysts suggest that while SoftBank's upcoming investments in AI and semiconductor technologies could improve profitability, execution risks remain high as investor enthusiasm for AI wanes. The company's stock has fallen by 38% in the September quarter, marking the most significant drop since 2001. SoftBank's quarterly results are anticipated soon, with expectations of only a slim profit amidst the volatility.