"You can invest in Japan with confidence,” Fumio Kishida, the country’s prime minister, told an international audience in London last week in a Japanese-language address, adding a three-word declaration in English almost as an exclamation point: "Invest in Kishida.”

The call seemed a throwback to speech by another Japanese leader — Shinzo Abe’s 2013 appeal at the New York Stock Exchange for investors to "Buy my Abenomics!” Abe’s rallying cry was, at least temporarily, a success. Foreign money flowed in during the early years of his premiership as investors bought into his narrative that Japan was back.

That story didn’t last as Abenomics ran out of gas. Only time will tell if Kishida will be more successful, though markets have so far paid it little heed, with the Nikkei 225 falling 2.4% since his speech amid a global market rout. But a comment by the world’s richest man just days after Kishida’s shows why the prime minister needs more than just a catchphrase to persuade investors of Japan’s long-term growth prospects.