Yuriko Gamo Romer's documentary "Diamond Diplomacy" traces 150 years of Japan-US relations through baseball, examining the sport's 1872 introduction to Japan by an American educator through its integration into schools, the rise of professional teams, and the eventual flow of Japanese players to Major League Baseball.
The film covers Babe Ruth's 1934 tour to Japan, the role of baseball for Japanese-Americans during and after World War Two internment, Negro League teams' visits to Japan, and the superstar status of players like Shohei Ohtani. Author Robert Whiting appears as a talking head, noting that Japanese baseball is older than judo and suggesting that perfectionist methods from martial arts shaped the sport in Japan.
Masanori Murakami, the first Japanese MLB player, anchors the film. He debuted for the San Francisco Giants against the New York Mets at Shea Stadium in September 1964 at age 19 and played alongside Willie Mays. At a screening before the film's official Japan premiere at Tokyo International Film Festival, Murakami recalled how his desire to move to the US was driven by his love of the cowboy drama "Rawhide." He described standing up to an umpire during a game in San Francisco and later receiving praise from a Japanese chef, who told him he was proud to see a Japanese person assert himself against an American.
Gamo Romer, born in Tokyo but raised in the US, started researching the film 12 years ago. After securing a $600,000 National Endowment for the Humanities grant, more than half was cancelled in April 2025 due to DOGE cuts. Former American diplomat Glen S. Fukushima provided $300,000 to allow the film to be finished.
Strand Releasing picked up the film for North America and Wondergenic for Japan.