A Thorough Explanation of the History and Current State of Mifune Castle (Kumamoto Prefecture) | Visiting the Ruins of the Castle of the Aso Clan and Kai Soun
What is Mifune Castle?
Mifune Castle was a medieval Japanese castle located in Mifune-cho, Kamimashiki-gun, Kumamoto Prefecture. Situated on a long, narrow hill approximately 40 meters east-west and 150 meters north-south, south of the current Mifune Elementary School, it was a flatland castle that served as an important base for the Aso clan in Higo Province.
The exact date of the castle’s construction is unclear, but it was already functioning as a castle in 1343 (Kōkoku 4), and records show that Aso Korezumi (Era Korezumi) defended it against an Ashikaga army invasion. This record indicates that it was established as a military base at least by the Nanboku-chō period.
Currently, the Mifune Castle ruins have been developed into Shiroyama Park, a place of relaxation for local residents. In spring, it’s a popular spot for cherry blossoms, attracting many visitors. From the small hill overlooking the town, you can enjoy a panoramic view of Mifune.
Basic Information about Mifune Castle
Location and Situated Area
Location: Mifune, Mifune-machi, Kamimashiki-gun, Kumamoto Prefecture
Former Province: Higo Province
Classification and Structure: Hilltop Castle
Keep Structure: None (As it is a medieval castle, there is no keep)
Common Name/Alternate Name
Mifune Castle doesn’t have a specific alternative name, and is sometimes called “Shiroyama” (Castle Mountain) locally. Because the castle ruins are now Shiroyama Park, it’s affectionately known as Shiroyama by locals.
Founder and Successive Lords
Founder: Unknown (Estimated to be a powerful local family of the Aso clan)
Main Successive Lords:
- Mifune clan (of the Aso clan lineage) (Nanboku-cho period to early Sengoku period)
- Mifune Fusayuki (Tenbun era)
- Kai Soun (Tenbun 10 / 1541 -)
- Kai Chikahide (Son of Soun)
History
Mifune Castle in the Nanboku-cho Period
The oldest record in the history of Mifune Castle dates back to the 4th year of Kōkoku (1343). In that year, Aso Korezumi, who was based in Yabe (present-day Yamato-cho, Kamimashiki-gun, Kumamoto Prefecture), is said to have defended Mifune Castle against an invasion by Ashikaga forces. During this period, there was intense power struggle between the Southern Court and the Northern Court (Ashikaga side) in Higo Province, and the Aso clan was active on the Southern Court’s side.
Mifune Castle was under the control of the Aso clan, and it is believed that the Mifune clan, a branch of the Aso clan, ruled this area as castle lords for generations. The place name “Mifune” itself is said to originate from the Mifune clan, a branch of the Aso clan, indicating a close connection between the castle and the region.
The Sengoku Period and the Era of Kai Soun
The most important turning point in the history of Mifune Castle occurred in 1541 (Tenbun 10). In that year, Mifune Fusayuki, the then-lord of the castle, rebelled against the Aso clan. Aso Koretoyo ordered his senior retainer, Kai Soun, to suppress Mifune Fusayuki, and Soun successfully accomplished this.
Kai Soun was a renowned warrior from Higo Province and served as the chief retainer of the Aso clan. For his achievement in defeating Mifune Fusayuki, Soun was granted Mifune Castle, and thereafter, Mifune Castle became the residence of the Kai clan.
Based at Mifune Castle, Soun acted as a mediator between the Aso and Otomo clans, demonstrating skillful diplomacy. At the time, Higo Province was under the influence of the Otomo clan of Bungo Province, and Soun played a crucial role in the Otomo clan’s control of Higo. His military talent and political acumen earned him the nickname “The Kirin of Higo.”
The Shimazu Invasion and the Defense of Mifune Castle
During the Tensho era (1573-1592), the powerful Shimazu clan of southern Kyushu began its northward advance, invading Higo Province. After the Otomo clan suffered a crushing defeat at the Battle of Mimikawa in 1578, their influence in Higo Province rapidly declined.
In this situation, Soun Kai found himself confronting the Shimazu army led by Shimazu Yoshihiro. Faced with the overwhelming military power of the Shimazu clan, many local lords in Higo Province surrendered, but Soun continued to resist from his base at Mifune Castle. However, he eventually succumbed to the Shimazu forces, and Mifune Castle also came under Shimazu control.
The Higo Provincial Uprising and the Downfall of the Kai Clan
In 1587, following Toyotomi Hideyoshi’s conquest of Kyushu, Higo Province was given to Sasa Narimasa. However, Narimasa’s forceful policies of controlling the local lords provoked resistance from the Higo people, and in the same year, a large-scale Higo provincial uprising broke out.
Kai Chikahide, the son of Kai Soun, is also believed to have participated in this uprising. The uprising put up fierce resistance, but Toyotomi Hideyoshi dispatched Kuroda Yoshitaka (Kuroda Kanbei) and others, ordering a thorough suppression of the rebellion. The uprising was suppressed, and many of the participating local lords were executed. Kai Chikahide was also executed, marking the end of the Kai family.
After the rebellion was suppressed, Sasa Narimasa was held responsible and ordered to commit seppuku (ritual suicide). Higo Province was divided, with the northern half given to Kato Kiyomasa and the southern half to Konishi Yukinaga. Kamimashiki District, where Mifune Castle was located, became Kato Kiyomasa’s territory, and it is believed that a castle guard was stationed at Mifune Castle.
After the Edo Period
It is presumed that in the Edo period, Mifune Castle ceased to function as a military base and gradually fell into disuse. This was because Kato Kiyomasa built Kumamoto Castle and made it his base, rendering small medieval castles like Mifune Castle unnecessary.
After the Meiji era, the castle ruins became a community-owned area and were eventually developed into a park. The current Shiroyama Park is carefully preserved as a place of relaxation for local residents and as a place to convey history.
Current Situation
Development as Shiroyama Park
Currently, the Mifune Castle ruins have been developed into Shiroyama Park and are open to the public. The park is located south of Mifune Town Mifune Elementary School, close to the town center and easily accessible.
A replica castle gate stands at the park entrance, giving visitors the impression that it is a castle site. This gate is not a historical relic, but was constructed for tourism purposes during the park’s development; however, it plays a role in creating the atmosphere of a castle site.
Status of Remains
Unfortunately, very few clear remains of Mifune Castle remain. Structures such as stone walls and moats cannot be confirmed, and traces of baileys and earthworks have been lost due to urbanization and park development.
The castle was built on a long, narrow hill, with the south and north sides slightly higher and sloping towards the center. This topography may indicate the original layout. Previously, a semicircular moat is said to have remained at the eastern foot of the castle, but it is now an urban area and its traces cannot be confirmed.
Within the park stands Shiroyama Tenmangu Shrine, which also functions as a place of worship for the local community. The area where this shrine stands may have been a major part of the former castle.
As a Cherry Blossom Spot
Shiroyama Park is known as a famous cherry blossom spot in Mifune Town. In spring, the entire park is adorned with cherry blossoms, attracting many visitors. Combined with the panoramic view of the town from the hilltop, it is a beloved cherry blossom viewing spot for local residents.
Local events are sometimes held during cherry blossom season, making it a good example of how a historical site can be utilized as a modern recreational area.
Access and Visiting Information
Access:
- Approximately 5 minutes by car from the Mifune Interchange on the Kyushu Expressway
- Approximately 30 minutes by car from Kumamoto City
- Within walking distance of the center of Mifune Town
Parking: Parking available around the park
Visiting Hours: Open all day (free to visit as it is a park)
Admission Fee: Free
Although there are few remains of the castle, visiting this historical site allows you to reflect on the situation in Higo Province during the Sengoku period and the achievements of Kai Soun.
Mifune Castle and Kai Soun
Indispensable to understanding Mifune Castle is Kai Soun, a renowned general of the Sengoku period. As a senior retainer of the Aso clan and lord of Mifune Castle, Soun left a significant mark on the history of Higo Province.
The Life of Kai Sōun
Kai Sōun (birth year unknown – around 1587) was a samurai from Higo Province and a senior retainer of the Aso clan. His real name was Kai Chikanao, and Sōun was his Buddhist name.
Sōun possessed exceptional military talent and achieved military success in numerous battles. In particular, his achievements in the subjugation of Mifune Fusayuki in 1541 earned him Mifune Castle, and he subsequently served as the chief retainer of the Aso clan.
Sōun’s greatest characteristic was his skillful diplomacy. At that time, Higo Province was under the influence of the Ōtomo clan, and the Aso clan needed to maintain relations with them. Sōun played a crucial role in mediating between the Aso and Ōtomo clans, stabilizing their relationship.
When the Shimazu clan advanced northward, Sōun also distinguished himself in battles against the Shimazu army, but ultimately he was forced to surrender in the face of the Shimazu’s overwhelming military power. However, his bravery and popularity were recognized by the Shimazu clan, allowing him to maintain a certain position.
Kai Chikahide and the Downfall of the Kai Family
Kai Chikahide, son of Soun, succeeded his father as lord of Mifune Castle. However, his participation in the Higo Province uprising in 1587 drastically changed the fate of the Kai family.
The uprising was thoroughly suppressed by Toyotomi Hideyoshi, and Chikahide was executed. This marked the end of the Kai family, who had ruled Mifune Castle for approximately 50 years since the subjugation of Mifune Fusayuki. The prestigious lineage built by Kai Soun came to an end.
Attractions Around Mifune Castle
Mifune Dinosaur Museum
Mifune Town is known as the “Village of Dinosaurs.” In 1979, the first fossilized tooth of a carnivorous dinosaur in Japan was discovered and named “Mifuneryu.” At the Mifune Dinosaur Museum, you can see exhibits of dinosaur fossils, including this discovery, and detailed information about dinosaurs.
Located just a few minutes’ drive from Shiroyama Park, it’s ideal for family sightseeing.
Mifune Terrace
This is a hot spring complex that opened in 2021 as a new tourist hub in Mifune Town. It’s a facility that integrates hot springs, restaurants, and a local products shop, allowing you to fully experience the charm of Mifune Town. It’s a convenient place to stop by after visiting the castle ruins.
One Piece Statue (Brook Statue)
Kumamoto Prefecture is the birthplace of Eiichiro Oda, the author of the popular manga “ONE PIECE.” As part of the recovery support after the Kumamoto earthquake, statues of the Straw Hat Pirates have been erected throughout the prefecture. Mifune Town has a Brook statue, making it a pilgrimage spot for fans.
Historical Significance of Mifune Castle
Mifune Castle is one of the castles that symbolize the history of Higo Province from the medieval period to the Sengoku period. Although no clear remains exist, its historical significance is considerable.
As a Base for the Higo Local Lords
Mifune Castle functioned as a base for the local lords (kokujin) in Higo Province. Controlled by the Mifune clan (a branch of the Aso clan) and later the Kai clan, Mifune Castle is crucial for understanding the political and military situation in Higo Province.
The Stage of the Power Struggle Between the Otomo and Shimazu Clans
During the Sengoku period in Kyushu, the Otomo clan of Bungo and the Shimazu clan of Satsuma vied for supremacy. Mifune Castle was located on the front lines of this power struggle, and Kai Soun skillfully conducted diplomacy and military operations in the midst of it all. The history of Mifune Castle provides valuable insights into understanding the Sengoku period in Kyushu.
The Stage of the Higo Local Lords’ Rebellion
The Higo Local Lords’ Rebellion of 1587 (Tensho 15) was a large-scale rebellion that shook the Toyotomi regime’s control over Kyushu. The fact that Kai Chikahide participated in the uprising and that the Kai family was destroyed demonstrates the strong control of the Toyotomi regime and the resistance of the local lords.
References
The following documents are useful for studying the history of Mifune Castle:
- *Place Names of Kumamoto Prefecture* (Heibonsha, Japanese Historical Place Names Encyclopedia)
- *History of Mifune Town* (Mifune Town History Compilation Committee)
- *History of Higo Province* (by Morimoto Kazumizu)
- *Famous Castles of Kyushu* (Gakken Publishing)
- *Local Lords of Higo Province in the Sengoku Period* (Kumamoto Prefectural Library)
- Various castle research books and local history research journals
These documents contain information on the construction period of Mifune Castle, its successive lords, its structure, and battle records, allowing for a multifaceted understanding of its history.
Summary
Mifune Castle was a medieval hilltop castle located in Mifune-cho, Kamimashiki-gun, Kumamoto Prefecture. It functioned as an important base in Higo Province from the Nanboku-cho period to the Sengoku period. The Mifune clan, a branch of the Aso clan, and the renowned general Kai Soun and his descendants served as lords of the castle, playing a crucial role in the power struggle between the Otomo and Shimazu clans.
In 1587, the Kai clan was destroyed in the Higo Provincial Uprising, and Mifune Castle disappeared from the historical stage. Currently, it is maintained as Shiroyama Park, and although no clear remains exist, it is a beloved place of relaxation for local residents, known for its cherry blossoms.
The history of Mifune Castle is a valuable example that tells the story of the rise and fall of regional powers in Kyushu during the Sengoku period, the power struggles between daimyo, and the process of unification under the Toyotomi regime. Visiting the castle ruins allows one to reflect on the lives of the warriors who lived through this turbulent era.
