As a private secretary he worked closely with Nobunaga not only on administrative matters but also on external issues with Shingen TAKEDA and due to a particularly amicable relationship with the Mouri family, TAKEI was appointed by Nobunaga and actively involved in negotiations between Takakage KOBAYAKAWA and Motoharu KIKKAWA etc.
秘書として信長そば近くに仕え、内政面だけではなく、外交面でも武田信玄、特に毛利家との友好関係のため小早川隆景、吉川元春らとの折衝にあたるなど、信長に重用され、活躍した。