Yamauchi Kazutoyo was a retainer to Oda Nobunaga (1534–1582) and participated in most major battles of the late sixteenth century under his command. His wife, Chiyo, was a daughter of the Gujo Hachiman Castle Lord located in modern-day Gifu.
According to local legend, she told Kazutoyo, “Love only me, and I will make your dream of becoming the lord of a domain come true.” When they were married, Chiyo had received ten pieces of gold from her family, which she kept secret from her husband. One day, a local horse dealer brought around an exceptionally fine horse. The horse was very expensive, and no one could buy it. Recognizing an opportunity to set her husband apart from the other retainers, Chiyo bought the horse with her secret gold. The new horse brought Kazutoyo to the attention of Nobunaga, who is believed to have said; “If no one within the Oda clan had bought this fine horse, it would have been an embarrassment. I’m glad you purchased it!”
Under Nobunaga, Kazutoyo would become master of the small Karakuni domain, and then Nagahama and Kakegawa castles. He later pledged allegiance to Tokugawa Ieyasu. Kazutoyo was awarded the lordship of Kochi Castle in Tosa Province in Shikoku for his help during the attack on Gifu Castle and the Battle of Sekigahara in 1600.