Yoshinaga Asano was the son of Nagamasa Asano, the daimyo of the Asano clan. He was born in Omi Province, and his first battle was the Fall of Odawara, serving as a common footsoldier, since he was only fourteen. In 1597, he took part in the Siege of Ulsan in Korea alongside his father, and after Hideyoshi died in 1598, he joined an Anti-Ishida Coalition led by Masanori Fukushima, aimed at slaying Mitsunari Ishida, who was attempting to restore the Toyotomi clan. Yoshinaga took part in the siege of Kyoto that year, where the coalition attempted to assassinate him, but they were beat off by the Uesugi, and they joined Ieyasu Tokugawa's opposing Eastern Army. Yoshinaga fought in the Battle of Sekigahara, and was entrusted with Omi Province as the leader of the Kishu Domain after the death of his father in 1611.