Yoshinobu enjoyed good relations with Ishida Mitsunari, whom he has assisted at the Siege of Oshi in 1590. He relocated his seat to Mito Castle, and contributed a large number of troops to Hideyoshi's subjugation of the Tohoku region, and a much smaller number of troops to Hideyoshi's Korean invasion, although he remained behind at Nagoya Castle and later at Fushimi Castle with Hideyoshi and did not cross over to the continent. Under Hideyoshi, his "kokudaka" gradually was increased to 545,765 "koku".