After arriving in Ryukyu, though initially faced with a number of difficulties, Manjiro's understanding of American motivations, as well as those of the Japanese, allowed him to serve as an interpreter during the treaty talks between the United States and the Empire of Japan.
その後、紆余曲折はあったが、日米和親条約の平和的締結に向け、通訳やアメリカの思惑や情勢を詳しく知る者として、時には裏方として尽力した。