The bakufu floundering in financial difficulties accepted Koitomi's advice and sent Soa as seishi and Koitomi as fukushi (vice envoy) to Ming, which had implemented isolationism, in 1401 to begin establishing relations with Ming.
財政難に苦しんでいた幕府は肥富の意見を取り入れ、1401年（応永8年）に祖阿を正使に、肥富を副使として鎖国中の明に遣わせ、日明の関係を開く糸口を作らせた。