TOKYO — A former Google executive and Silicon Valley star was on course to be the next chief executive of SoftBank of Japan, one of the world’s most prominent technology conglomerates. Now he is leaving, in an abrupt shakeout that shows cracks in SoftBank’s global ambitions.

When the executive, Nikesh Arora, was poached two years ago from a coveted role as Google’s head of business operations, the hire was widely considered a coup for SoftBank. Its billionaire founder and chief executive, Masayoshi Son, crowned Mr. Arora heir apparent.

Mr. Arora was vaunted for his deal-making prowess and seen as an international executive who would help transform SoftBank with a flurry of investments. One of Mr. Son’s most cherished ambitions was to turn SoftBank, a Japanese business with some notable overseas names like the American carrier Sprint, into a truly global enterprise.

The honeymoon did not last.

Investors have criticized Mr. Arora recently for his record of managing SoftBank’s overseas deals. Investments in start-ups like DramaFever and Housing.com, these shareholders have said, appear to have soured as the companies have faltered.