The Battle of Otsu-jo Castle (大津城の戦い)
The Battle of Otsu-jo Castle took place from October 13, 1600 to October 21, 1600.
After Hideyoshi TOYOTOMI died, the opposition between Ieyasu TOKUGAWA, who set out to rule the world, Mitsunari ISHIDA, a defender of the Toyotomi clan and member of the anti-Ieyasu group, came to the forefront in the wake of the attack on Aizu in 1600. Taking the opportunity presented by Ieyasu leaving to attack Aizu, Mitsunari ISHIDA rallied anti-Ieyasu daimyos (feudal lords) such as Yoshitsugu OTANI and Terumoto MORI and took up arms. He then captured the Fushiki-jo Castle exploiting Ieyasu's absence from the Kinai region (provinces surrounding Kyoto and Nara), and after that he set out to suppress the Hokuriku region and Ise area in Ise Province.
Yoshitsugu OTANI, who was a daimyo in Tsuruga, Echizen Province, assisted with the suppression of the Hokuriku area. And as a member of the Hokuriku area force Takatsugu KYOGOKU, the lord of Otsu-jo Castle in Omi Province, was part of the Yoshitsugu army. However, while Yoshitsugu was changing his course from the Hokuriku area to Mino Province, Takatsugu suddenly switched to the East side, led his 3,000 soldiers to Otsu-jo Castle and fortified the defenses there. Yodo-dono (Lady Yodo; Hideyoshi TOYOTOMI's concubine and the mother of Hideyori, the heir to the Toyotomi clan) was surprised to hear of this treachery and dispatched an envoy to Takatsugu's wife (Yodo-dono's younger sister Hatsu/Joko-in was at Otsu-jo Castle as she was Takatsugu's lawful wife) to call for a truce and surrender, but the Otsu side never accepted it.
In response, the West squad started to besiege Otsu-jo Castle on October 13, 1600 with a force of 15,000 strong mainly organized by daimyos in the Kyushu areas such as Muneshige TACHIBANA, Hidekane MORI and Hirokado TSUKUSHI and led by Motoyasu MORI in retribution for Takatsugu's treachery. However, Takatsugu defended the castle to the last and the siege made poor progress. People who took an especially active role included Akao Izu no kami and Oi YAMADA, who are said to have sallied forth from the castle with 500 elite warriors and stormed their enemy. The offensive force were at a loss on how to continue, and fired cannons at the castle on October 19. The artillery shells hit the main tower of the castle and caused havoc inside. Takatsugu defended fiercely, but a spearhead convoy led by Kichiemon TACHIBANA from the Tachibana force reached the castle walls.
Takatsugu and other Kyogoku forces fought to the last, but eventually became exhausted and surrendered the castle on October 21st. Takatsugu's life was spared and he entered into priesthood at the Koyasan (Mt. Koya) temple.
The West squad won tactically at this siege of Otsu-jo Castle but was defeated strategically. This is because October 21, 1600, when Takatsugu surrendered Otsu-jo Castle, was the very day that the Battle of Sekigahara took place. Which means that the West squad was forced to fight with the disadvantage of fighting against the East squad without the 15,000 warriors that should have been deployed to Sekigahara. The lack of participation by Muneshige TACHIBANA at Sekigahara was especially lucky for Ieyasu and unlucky for the West squad because Ieyasu feared Muneshige's gallantry in action. There is the possibility that if Muneshige had joined the Battle of Sekigahara with a force of more than 10,000, the outcome of the battle may have been different. In fact, after Muneshige had made Takatsugu surrender Otsu-jo Castle on October 21, he and his troops advanced to Kusatsu city, where he knew of the defeat of the West squad and was forced to retreat to Osaka-jo Castle; because of this, after the battle he forfeited the rank of Samurai and his properties.
On the other hand, Takatsugu KYOGOKU received great praise from Ieyasu for attracting Muneshige TACHIBANA to Otsu-jo Castle and containing him there, so much so that after the Battle of Sekigahara he sent Takatomo KYOGOKU, Takatsugu's younger brother, to Koyasan and not only allowed him to return as a daimyo but also gave him the territories of Obama-jo Castle, comprised of 92,000 koku (unit), in Wakasa Province.