SoftBank Group¡¯s swelling weight in Japan¡¯s equity benchmark is pushing even its skeptics to buy the stock.

Founder Masayoshi Son¡¯s bets on artificial intelligence have fueled a 146% surge in the stock since the fiscal year began in April, making it one of the Topix¡¯s top performers. SoftBank¡¯s weight in the gauge has doubled to 2% over the period, just behind blue chips such as Toyota Motor and Sony Group.

Despite concerns over SoftBank¡¯s volatility and complex business model, fund managers need to hold it if they want to beat the market, according to Yoshiki Nagata, chief investment officer at enTorch Capital Partners.