Because of its opposition to the Imagawa clan, Yoshiyasu supported the Oda clan in Owari Province who was also resisting the Imagawa clan, then started to maintain the defense system.
義安は今川氏への対抗上、同じく今川氏と抗争中にあった尾張国の織田氏に加担し、防衛体制を整えていく。