When the giants of sumo wrestling prepared to step into the ring for last month's grand tournament in Tokyo, Akiyoshi Takumori fired up his spreadsheet.

For Takumori, an economist at one of Japan's biggest asset managers, the ancient sport is more than entertainment: It is an eye into how successful Prime Minister Shinzo Abe has been at unleashing the country's animal spirits.

By counting the number of advertisements paraded before bouts — company names embroidered on banners and carried around the ring by a posse of men in kimono — investors can gauge whether executives are bullish on the economy and willing to spend their companies' cash, Takumori says.