When the third Seii taishogun Yoshimitsu ASHIKAGA of the Muromachi bakufu (Japanese feudal government headed by a shogun) tried to do trade with the Ming Dynasty, he was rejected because he was the emperor's vassal; therefore, he was given the title of Jusangu and with the diplomatic title of Japan Jugo, he sent a Japanese envoy to China during the Ming Dynasty; thus, Jugo were politicized for the purpose trading, by receiving the title of Japanese king and approval for tribute trade.
室町幕府3代征夷大将軍足利義満が明との勘合貿易を目論んだ際は、臣下であるとして拒否されたため、准三宮宣下を受けて日本国准后の外交称号で遣明使を派遣、日本国王の封号と朝貢貿易の許しを得て巨万の富を得るなど政治的に利用されるようになった。