BANGALORE, INDIA – SoftBank Group Corp. plans to announce within days that it will start a mobile digital payments service in Japan by the end of 2018, as billionaire founder Masayoshi Son seeks to expand in the sector, people familiar with the matter said. The service, a collaboration with Indian startup Paytm, will make extensive use of artificial intelligence for mobile payments and other financial services, the people said, asking to not be identified as the plans are private. An announcement is imminent, they said. Dozens of Paytm employees are working in Tokyo on getting the service up and running, one of the people said. Son, who created the world's largest technology investment fund, is moving into a crowded field as local banks and technology companies rush to stake their claims.