When Masayoshi Son and Sam Altman first met each other in 2017 at SoftBank’s offices in Tokyo, the younger entrepreneur lacked a project large enough to tempt the tech billionaire to get his cheque book out.

SoftBank Group Corp. tumbled to a loss in the December quarter, weighed down by a drop in the value of the Vision Fund’s public holdings, just as Masayoshi Son campaigns to raise $500 billion for the Stargate artificial-intelligence project.