Having the confidence of Yoshimitsu and his sons, the fourth shogun Yoshimochi ASHIKAGA and the sixth shogun Yoshinori ASHIKAGA, Mansai was deeply involved in the internal politics and diplomacy of the shogunate government and was nicknamed Kokui no saisho (a priest who has influence in politics).
義満とその子である4代将軍足利義持・6代将軍足利義教の信任が厚く、内政･外交などの幕政に深く関与し、黒衣の宰相と称された。