In 1554, the daughter of Yoshimoto IMAGAWA married his legitimate son, Yoshinobu as his lawful wife to enhance the Kosun Alliance (an alliance between the Takeda clan in Kai Province and the Imagawa clan in Suruga Province).
天文23年（1554年）には嫡男義信の正室に今川義元の娘を迎え、甲駿同盟を強化する。