The app was first rolled out in September in Osaka, a popular destination for Chinese tourists, where it has tied up with 40 taxi firms in an increasingly crowded market for such apps that includes rivals backed by Sony and Toyota Motor.
It is expanding into Tokyo and Kyoto from Wednesday, with a further 10 locations to follow in the current financial year.
Despite SoftBank's oversized presence in the global ride-hailing industry, such services are effectively banned in Japan, leaving SoftBank portfolio companies like Didi and Uber limited to offering services that match taxis with customers.
Didi is among a growing number of SoftBank Group Corp-backed companies launching JVs with SoftBank's domestic telco.
Other startups doing so are shared co-working firm WeWork Cos and Indian hotel startup OYO.
As part of SoftBank's efforts to drive synergies between its portfolio companies users will be able to access the taxi-hailing service through Yahoo Japan's route-finding app and pay via PayPay, an app that uses tech from India's Paytm.