SoftBank’s Heavy Weight Forces Skeptical Stock Investors to Buy

SoftBank Group Corp.’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 bluechips such as Toyota Motor Corp. and Sony Group Corp. 

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.

“A lot of institutional investors are now agonizing over how to deal with SoftBank,” he said. “If you don’t own this particular stock, all the effort to pick other good investments goes to waste.”

SoftBank shares provided almost 10% of the increase in the Topix’s market capitalization since the end of March, as Son’s tech and telecoms empire’s value increased by 15.9 trillion yen . The next highest contributors to the benchmark — Advantest Corp. and Mitsubishi Heavy Industries Ltd. — supplied less than half of that. 

Investors need to realize that Softbank’s stake in OpenAI will increasingly impact its valuation, said Hiroaki Tomori, executive fund manager at Mitsubishi UFJ Asset Management. OpenAI’s big spending plans are already boosting US tech shares such as Broadcom Inc. and Oracle Corp.

“OpenAI’s growth is staggering, the use of AI is becoming ubiquitous,” he said. “We should see a sign of confidence behind the big orders OpenAI is making.” 

While SoftBank shares tend to outperform when the market is in an upswing, they are vulnerable during downtrends. The stock’s beta, a measure of how much it moves relative to the entire market, is the highest among the top 100 Japanese companies at 1.515, meaning it moves 1.5 times more than the index. 

Based on Bloomberg data, SoftBank shares now trade at about a 20% discount to net asset value — the narrowest gap in years — fueling speculation the rally could stall at the first sign of weak investments. 

Still, Son’s latest spending spree, from a fresh $30 billion commitment to Stargate artificial intelligence initiative with OpenAI to a surprise $2 billion bet on Intel Corp., is instilling renewed optimism.

Daisaku Masuno, an analyst at Nomura Securities Co., is forecasting the discount will disappear, as an improvement in its Vision Fund’s investments has reduced risks and its AI chip initiative looks more likely to make progress. He raised his target price twice for SoftBank shares in less than a month, expecting a 0% NAV discount.

Meanwhile, gains in SoftBank shares may accelerate as some investors continue to bring their underweight positions in the stock back to par with the benchmark, according to EnTorch Capital’s Nagata. 

“When a share with a big weight like SoftBank keeps rising, it is hard to close your underweight position,” he said. “This is a structural problem with benchmark-linked investment. We could see a self-feeding loop of additional buying inviting more buying.” 

©2025 Bloomberg L.P.

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