The franchise originated in the Japanese Baseball League (NPB's predecessor) and existed from 1936–1953, when it merged with the Taiyo Whales.

[citation needed] Late in the 1940 season, the Japan Baseball League outlawed English nicknames (due to rising tensions with the West).

)[citation needed] The team completed the season as Lion, finishing in last place, 50 games behind Tokyo Kyojin.

[citation needed] To fill out its roster, Pacific signed long-time Tokyo Kyojin/Yomiuri Giants pitcher Victor Starffin, as well as some other famous players.

In 1950, when the JBL reorganized to become Nippon Professional Baseball, the Robins joined NPB's Central League.

Led by league MVP Makoto Kozuru and his 51 home runs and still-league record 163 RBI, as well as Sanada's 39 victories, the Robins played in the inaugural Japan Series, ultimately falling to the Mainichi Orions, 4 games to 2.