Suzuki, Mazda, Subaru, Isuzu Motors and Toyota's compact car unit Daihatsu will each invest 57.1 million yen ($530,620) in the venture — dubbed Monet — in return for a 2% stake, the companies said in a statement.
SoftBank and Toyota will each retain their 35% stakes in the company, which is now capitalized at $26.6 million. The latest investors join Honda Motor and Hino Motors, Toyota's truck-making operations, which each own 10% stakes.
Launched in October, the venture plans to roll out on-demand bus and car services in Japan in the next year, and a services platform for electric vehicles in the country as early as 2023 based on Toyota's boxy "e-palette" multi-purpose vehicle.
Monet is building up members as it joins the ride-sharing sphere which is dominated by startups such as Uber Technologies, Didi Chuxing and Lyft, as traditional automakers band together to compete in an industry which is placing growing emphasis on offering vehicle services rather than selling cars to individual drivers.
Automakers are increasingly joining forces with technology companies as well as each other as they grapple with the massive investment and software expertise required to develop these new services for which demand has yet to be tested.
The new investment will see Suzuki, Mazda and Subaru deepen their partnership with Toyota, as they have already agreed to tap the R&D firepower of Japan's biggest automaker for electric cars and other future vehicle technologies.
Friday's announcement comes after Monet's chief executive told Reuters earlier this month it was planning to expand its investor base and start operating in Southeast Asia next year.