Lifespan: Tenshō (1576) to 8/17 of Keichō 7 (1602)
Other Names: Genjirō
Lord: Shimazu Tadatsune
Father: Ijūin Tadamune
Siblings: Tadazane, Kodenji, Kimotsuki Kanehiro, Senji
Wife: Oshita (second daughter of Shimazu Yoshihiro)
Children: Chizuru (adopted daughter of Shimazu Tadatsune, dowager of Matsudaira Sadayuki)
Ijūin Tadazane served as a bushō during the Azuchi-Momoyama period. He was a retainer of the Shimazu clan.
In 1576, Tadazane was born as the lineal heir of Ijūin Tadamune, a retainer of the Shimazu clan of Satsuma Province.
Tadazane also served as a retainer of the Shimazu family. He deployed for the Keichō Campaign on the Korean Peninsula. In 1598, at the Battle of Sacheon, Tadazane’s division captured over 6,500 heads. In 1599, his father, Tadamune, wielded his authority with abandon and was murdered by Shimazu Tadatsune at the Shimazu residence in Fushimi. After succeeding his father as the head of the clan, Tadazane holed-up in Miyakono Castle in Shōnai in Hyūga Province and openly revolted against the Shimazu in an event known as the Shōnai Rebellion.
In 1600, through the mediation of Tokugawa Ieyasu, the parties temporarily settled, but Tadazane later betrayed the Shimazu again. This occurred when Tadazane sought to separate from the Shimazu clan and enter into service for another family, but Tadatsune was firmly opposed. Ieyasu mediated a second time and the two sides reconciled on the condition that Tadatsune grant landholdings of 10,000 koku in Ei to Tadazane. Finally, Tadazane returned to the service of the Shimazu clan, wed the second daughter of Shimazu Yoshihiro and, after the rebellion, appears to have resided at Yoshihiro’s residence. Nevertheless, after returning to the service of the Shimazu, Shimazu Yoshihisa and Tadatsune remained vigilant of Tadazane. In the prelude to the Battle of Sekigahara, Yoshihiro deployed for the main battle and repeatedly demanded the dispatch of troops from Satsuma, but, out of fear of a rebellion, the clan did not send troops. Consequently, Yoshihiro did not command a large army befitting of a major daimyō and, owing to the absence of forces, struggled in battle.
In 1602, Tadatsune planned to travel to Fushimi to apologize for the failure by the Shimazu to adequately deploy for the Battle of Sekigahara and Tadazane agreed to accompany him, but then, while Tadazane was engaged in a hunting expedition in Nojiri in Hyūga, he was shot to death upon orders of Tadatsune. Meanwhile, his younger brothers (Kodenji, Saburō-Gorō, and Senji) and his mother who, after the Shōnai Rebellion, each took refuge in separate residences of retainers of the Shimazu family, were all killed and the remainder of the Ijūin family purged in their entirety. The slaying of Tadazane was characterized as an errant discharge of a firearm by Fuchiwaki Hirauma for which Hirauma was ordered to commit seppuku. Several years later, surviving family members were promoted to the position of high-ranking retainers. This appeared as recompense to the Ijūin by the Shimazu.
Tadazane did not have a son but had one daughter named Chizuru. After the death of Tadazane, she was adopted by Tadatsune and became a dowager of Matsudaira Sadayuki. His wife, Oshita, wed Shimazu Hisamoto.
Reasons given for Shimazu Tadatsune to purge the Ijūin family include that (i) Tadazane divided Yoshihisa and Yoshihiro and attempted to align with Yoshihiro, and (ii) Kodenji leaked to Yoshihiro information from Yoshihisa.
Others surmise that Tadatsune purged the Ijūin family that was detested by the members of the Shimazu to receive recognition from Yoshihisa and the retainers of the benefit from his travel to the capital.