To help implement his vision, Son also allied with General Motors Co. and Honda Motor Co., each of which is investing heavily in self-driving vehicles and ride services.
Son laid out his future of transportation vision in an October press conference alongside Toyota, where he talked about building a "cluster" of leading mobility companies in different sectors, which "can collaborate with each other."
Toyota a year ago introduced e-Palette, an electric shuttle designed for self-driving ride and delivery services, and quickly signed up Uber and Didi as development partners. The e-Palette is also the centerpiece of Monet Technologies, which added Honda as a minority partner in March. All are tied back to SoftBank.
That collaboration is expected to enable some SoftBank companies to become "superapps," or applications where customers go for a range of services, such as transportation, shopping and payments. Such companies can be much more lucrative than those that offer just one core business or service.
But the fact that many of SoftBank's companies are rivals can complicate the investor's ambitions. Uber and Ola, the Indian ride-hailing company, remain fierce competitors and are never in the same room when SoftBank discusses ride-hailing strategies, Claure said.
Traditionally in venture capital, funds do not invest in direct competitors.
"There are tremendous synergies, but on the other hand there is significant risk of tremendous conflicts of interest," said Paul Asel, managing partner at NGP Capital and a longtime mobility investor.
There are limits to the investor's influence, however. For example, SoftBank encouraged Cruise to acquire or take a stake in self-driving startup Nuro, but talks between the companies never led to a deal, according to two sources with knowledge of the matter.
So SoftBank made its own, $940 million investment in Nuro.
Hunting big game
In his five-year transportation push, Son's stakes in ride services startups now look like bargains. In late 2014, SoftBank joined Alibaba, China's internet giant in which SoftBank also has a stake, in a $600 million funding round in Kuaidi Dache, the forerunner of China's Didi.
That investment has grown to more than $11 billion in Didi, in which SoftBank now holds more than 20 percent.
SoftBank's partnerships with major automakers are also proving to be a boon to transportation startups. Toyota invested in Uber in 2016, then boosted its stake seven months after SoftBank's investment. Honda followed SoftBank with an investment into Grab, and last year committed $2.75 billion to Cruise's self-driving project, aiding SoftBank's ambitions.
But the SoftBank portfolio is not without risks, particularly for companies dependent on the Japanese firm to sustain them financially for years to come. SoftBank faces financial pressures, including an obligation to pay an annual 7 percent dividend on a portion of the invested capital and has burnt through the majority of the Vision Fund.
And it is compelled by a new U.S. law cracking down on foreign investment in technology to submit many of its mobility investments to a government regulatory agency for approval. Should that regulatory group block a deal, it could be catastrophic to a startup.
But there is some safety for Son given the size of his portfolio.
"He's shooting for big game," Roger Lanctot, global automotive practice director at Strategy Analytics, said of Son. "He only needs to bag one or two and he will do just fine."