This hypothesis states that Kozusu was the reason why Mitsunari's second daughter was taken in by Kanetsugu NAOE and married to his nephew's wife's brother, Hanbe Shigemasa OKA (Hideyuki GAMO and Tadasato GAMO's chief retainer and grandfather of Iemitsu TOKUGAWA's concubine, Jishoin) and that she conducted negotiations over the surrender of Otsu-jo Castle during the Battle of Sekigahara.
三成の次女を直江兼続に託し、甥の妻の兄弟である岡半兵衛重政（蒲生秀行・蒲生忠郷の家老、徳川家光側室・自証院の祖父）に嫁がせたのも、関ヶ原合戦時に大津城の開城交渉にあたったのも孝蔵主とする。