The easygoing Matsumura, who speaks English well and has a natural sense of humor, merged easily into life in the United States. But company insiders and analysts say the upbeat and charming Shiga is the lead candidate.
Takaki Nakanishi at UBS Warburg (Japan) Ltd. said: "I will bet on Mr. Shiga. He's young and cheerful."
Nissan executives say Shiga's personality is closest to that of the confidence-inspiring Ghosn - considered a crucial asset.
Even more important are Shiga's French connections. After working in Nissan's Asian operations and corporate planning, he helped negotiate the 1999 deal that led Renault to take its initial 36.8 percent, now 44.4 percent, stake in Nissan.
"He is trusted by Renault," said an industry source close to him. "And he is loyal to Renault."
Shiga caught Ghosn's eye early. In 2000, Ghosn elevated Shiga, then general manager of the corporate planning department and alliance coordination office, to senior vice president. At 46, he was the youngest-ever senior vice president among Nissan's Japanese employees. Last year, Ghosn made him a member of the executive committee, Nissan's supreme decision-making body.
Shiga is the youngest person on the eight-member committee.
He is "Ghosn's child," said an analyst at a foreign brokerage in Japan.
Shiga earned the promotion. In the three years since he took over what Nissan calls general overseas markets, unit sales in his areas have grown by 22 percent. That is ahead of Nissan's performance in Europe and the United States.
A Nissan insider described Shiga as "clever," with an ability to "figure things out." Another former Nissan employee called him obedient: "He wouldn't say 'no' to his bosses."
And Shiga gets points for being able to get along well with Ghosn. That could be one of the most important qualifications for a COO serving an absentee CEO.
Ghosn's successor "will have to be able to get into Ghosn's frame of mind," said Koji Endo, an analyst at Credit Suisse First Boston in Japan.