Siege of Ōtsu Castle

From September 7 to 15 in Keicho 5 (1600), the "Battle of Ōtsu Castle," which unfolded at Ōtsu Castle in Ōmi Province (present-day Ōtsu City, Shiga Prefecture), is known as the siege battle with the most dramatic conclusion among the preliminary engagements of the Battle of Sekigahara. Garrison commander Kyōgoku Takatsugu led approximately 3,000 soldiers who fought continuously for nine days against approximately 15,000 elite Western Army forces under Tachibana Muneshige and others, finally opening the castle on the very day of the main Battle of Sekigahara (September 15). This narrow time difference decisively influenced the outcome of the Battle of Sekigahara — this is how later historians have evaluated it.

Kyōgoku Takatsugu — The Shame of the "Firefly Lord" and His Restoration of Honor

Kyōgoku Takatsugu (1568–1614) was born into the prestigious Kyōgoku family of the Ōmi-Genji and served as a daimyo of Ōtsu in Ōmi Province under the Toyotomi regime.

Takatsugu's reputation was complex both during and after his lifetime. Known for his beauty, he had ties to the Toyotomi family through his marriage to Jōkō-in, the sister of Yodogimi, consort to Hideyoshi. However, having achieved little as a military commander, he was mocked as the "firefly lord" (hotaru daimyō) — a figure who shone not by his own abilities but by the reflection of others' light.

Yet on the eve of Sekigahara in Keicho 5 (1600), Takatsugu made a momentous decision. Though initially appearing to side with the Western Army, at the critical moment he announced his switch to the Eastern Army (the Tokugawa faction) and defended Ōtsu Castle against the Western forces. Multiple theories explain this reversal — a sense of obligation to the East, personal trust in Tokugawa Ieyasu, and dissatisfaction with the Osaka Toyotomi are said to have converged.

The final light that the "firefly lord" shed took the form of a nine-day siege, and he came to be praised by later generations for his strategic contribution to history.

The Course of the Battle of Ōtsu Castle — Nine Days of Attack and Defense

On September 7 of Keicho 5, Tachibana Muneshige, Mōri Motoyasu, Tsukushi Hiromado, and other Western Army commanders surrounded Ōtsu Castle. For the Western Army, the capture of Ōtsu Castle was essential to secure their rear. Ōtsu was a strategic crossroads connecting Kyoto and Ōmi; if an enemy castle remained there, the Western Army's lines of communication would be threatened.

Ōtsu Castle was a water fortress situated on the shore of Lake Biwa, which provided certain defensive advantages. Yet the disparity in forces — 3,000 versus 15,000 — was stark, and a prolonged siege had clear limits.

Tachibana Muneshige was renowned as one of the finest generals of Kyushu and had distinguished himself in the Korean campaigns. That this formidable Muneshige continued to struggle against Ōtsu Castle speaks to the high quality of Kyōgoku Takatsugu's defense. The Western Army reportedly brought artillery and bombarded the castle walls and stone ramparts. After nine days of fierce combat, on September 15 Ōtsu Castle surrendered.

That this surrender fell on the same day as the main Battle of Sekigahara was not chance but historical irony. The 15,000 elite Western Army forces under Tachibana Muneshige and others were pinned down at Ōtsu until the very day the decision at Sekigahara was made. The question—if Ōtsu Castle had fallen earlier and Muneshige's forces had reached Sekigahara in time—remains one that historians of Japan continue to pose.

Tachibana Muneshige — The "Undefeated General" Before and After Sekigahara

Tachibana Muneshige (1567–1643) became successor to the Tachibana family as the adopted son-in-law of Betki Dōsetsu, a renowned general of Kyushu, and is known as a "general of righteousness" and "undefeated general" at the end of the Sengoku period.

Muneshige is renowned as one of the Japanese warriors who fought most courageously on the Korean peninsula during the Bunroku and Keicho campaigns. At the Battle of Byeokjegwan in 1593, he defeated a large Ming army. The fact that this Muneshige struggled with the assault on Ōtsu Castle and failed to reach Sekigahara in time underscores the quality of Takatsugu's defense.

After Sekigahara, Muneshige, having sided with the Western Army, lost his position as daimyo. However, because of his great reputation, the Edo shogunate later restored him to favor, and he eventually returned to his former domains in Yanagawa Han (present-day Yanagawa City, Fukuoka Prefecture). Muneshige's life—as the "sole external daimyo to recover former domains once lost"—exemplifies the fate of generals during the late Sengoku and early Edo periods.

Regarding the swords favored by Muneshige, he is said to have preferred works by famous swordsmiths of Chikuzen Province, a major swordmaking center of Kyushu. His connections with swordsmiths of Kyushu origin, such as Horikawa Kunihiro, are also documented, and Muneshige occupies an important position as a bearer of Kyushu sword culture.

The Battle of Ōtsu Castle from the Perspective of Japanese Swords — Ōmi Blades and Sword Culture in the Sekigahara Era

Ōmi Province (present-day Shiga Prefecture), the stage of the Battle of Ōtsu Castle, was not a major center of Japanese sword production, but held special significance as a crucial crossroads of sword trade and distribution.

Ōmi Province lay at the intersection of the Tōkaidō, Hokuriku, and Nakasendō roads and served as a logistics hub connecting Kyoto with the provinces. Fine swords from Bizen, Mino, and Yamato circulated nationwide via Ōmi, and daimyo traveling to Kyoto passed through the region. The Kyōgoku family, the ruling house of Ōmi, is thought to have been involved in the curation and distribution of many renowned blades.

By Keicho 5 (1600), the forces that Tachibana Muneshige commanded in the assault on Ōtsu Castle included warriors from diverse regions—Kyushu, Chūgoku, and Kinai—each carrying swords made by different regional swordsmiths. The battlefield of Ōtsu Castle was precisely a place where the sword cultures of all Japan converged.

The swords borne by the warriors who distinguished themselves in Kyōgoku Takatsugu's defense are thought to have included not only works by local Ōmi smiths but also masterpieces from the Bizen, Mino, and Sōshū traditions. Through nine days of violent combat, each warrior's "precious blade"—the sword of the soul—shone brightly in the land of Ōmi.

The Historical Significance of the Battle of Ōtsu Castle — The "What If" That Changed Sekigahara

The special historical importance of the Battle of Ōtsu Castle lies in its "what if" possibility.

If Kyōgoku Takatsugu had not defended Ōtsu Castle—if he had sided with the Western Army—the 15,000 elite forces under Tachibana Muneshige might have been able to participate at Sekigahara. In the main Sekigahara engagement, the Western Army roughly matched the Eastern Army in number, but the Eastern Army achieved decisive victory when Kobayakawa Hideaki defected to their cause. Had Muneshige's 15,000 elite forces been added to the Western side, the outcome of Sekigahara might have differed—at minimum, the swift and overwhelming Eastern victory might not have occurred.

Takatsugu's shame as the "firefly lord" completely disappeared through the nine days of defending Ōtsu Castle, and later historians came to evaluate him as a "hidden contributor to Sekigahara." The "firefly lord" transformed on the eve of Sekigahara into the "bonfire lord" (kagaribi daimyō)—a great flame that illuminates the night.

Ōtsu Castle in the Modern Era — As a Disseminator of Ōmi History

Ōtsu Castle was dismantled in Keicho 7 (1602) after Sekigahara, and its materials were used in the construction of Zeze Castle. Today, little remains of Ōtsu Castle in the Hamaōtsu area of modern Ōtsu City, but the Ōtsu City Historical Museum displays materials related to Kyōgoku Takatsugu and the Battle of Ōtsu Castle, with explanations of Ōtsu Castle's place as a preliminary engagement to Sekigahara.

Ōmi Province borders Gifu Prefecture, the site of the Battle of Sekigahara, and is about an hour's drive from Ōtsu to the battlefield. The historical route through "the three sites of the Sekigahara preliminary engagement"—Ōtsu Castle ruins, Sekigahara Battlefield, and Gifu Castle—is one of the finest ways to experience the battles of the late Sengoku period.

For enthusiasts of Japanese swords, many blades connected to warriors involved in Sekigahara are scattered across museums nationwide, and a "sword pilgrimage" through Ōtsu, Sekigahara, and Gifu is also a journey into deep understanding of the samurai code of honor before the Edo period. From the land of Ōtsu, which Takatsugu defended for nine days before opening its gates, imagining history's "what if" provides the most vivid understanding of an age in which the Japanese sword shone brilliantly.