LONDON — SoftBank, the Japanese technology investment giant, is facing pressure from an unexpected source: a titan of the hedge fund world.

Elliott Management, the $40.2 billion hedge fund run by Paul E. Singer, has taken a $2.5 billion stake in SoftBank and has been urging changes at the company, three people familiar with the matter said on Thursday. Those moves could include stock buybacks, changes to SoftBank’s board or increased transparency for its $100 billion Vision Fund, the tech patron that has suffered huge black eyes in recent months.

Under its outspoken and ambitious founder, Masayoshi Son, SoftBank has set its sights on technology that will define the future, from artificial intelligence to ride-hailing. Much of that investing is done through the Vision Fund, driven by Mr. Son’s instinctive approach. He has been known to approve an eight-figure investment after a single meeting with a founder.

But SoftBank has been humbled by the near-collapse of WeWork, the office-sharing company, which it was forced to bail out after a failed attempt to go public in September. Several other start-ups that the Vision Fund has invested in — including Uber, the Indian hospitality start-up Oyo and the robotic pizza company Zume — have recently announced layoffs or scaled back their ambitions. In December, SoftBank sold its interest in the dog-walking start-up Wag at a loss after it laid off workers.