The Aso Clan (阿蘇氏)
The Aso clan originated in Higo Province.
It is believed that the ancestors of the Aso clan served as priests that worshipped the God of Mt. Aso and later became gozoku, or a local ruling family. This priest-gozoku clan then seemed to have served the Yamato dynasty, offered its territories, and became agatanushi, or a territorial ruler. Then, the clan gained power as Asonokuni no miyatsuko (head of the Aso government) when there was an administrative transition from the prefecture system to the Kuninomiyatsuko (local government) system. According to "Kujihoongi" (Ancient Japanese History), Hayamikatama no mikoto, who was Takeiwa tatsuno-mikoto's child, was the first Asonokuni no miyatsuko. There is in fact the Kokuzo-jinja Shrine that enshrines Hayamikatama no mikoto.
Takeiwa tatsuno-mikoto is believed to be a child of Kamuyaimimi no mikoto. However, it was often the case that a local gozoku that submitted itself to the Imperial Court was considered as a descendent of Kamuyaimimi no mikoto, and the case of Takeiwa tatsuno-mikoto is probably one such example.
What Takeiwa tatsuno-mikoto really was to start with was a volcano. Takeiwa means a huge rock (there is a record that it fell into a crater lake). The name Takeiwa tatsuno-mikoto was the combination of two beliefs, one is for the huge rock, and the other is for a dragon (the ruler of the crater lake and also the God of water and rain). Each time a natural phenomenon such as eruption, light emission, or changes in the crater lake occurred, it was reported to the central government as a phenomenon caused by a Shinto god, resulting in a raise of shinkai (a rank granted to Shinto gods) and granting of fuko (residential units (ko) assigned as prebends (fu) to support top-ranking officials, temples, shrines, and royal households such as those of the queen-consort and crown prince). Records of these beliefs in Mt. Aso, rites, and festivals are contained in Zuisho-wakoku-den (Chronicles of the Sui Dynasty). The Aso clan served as a Shinto priest family that managed the Mt. Aso beliefs.
From the generation of ASO no Tomonari (UJI no Tomonari) who lived in the Engi era, the Aso clan inherited the position of daiguji (high priest of a great shrine) of Aso-jinja Shrine. Then, the clan gained power not only in rites and festivals but also in politics, and became a daimyo (Japanese feudal lord) clan. The clan was subject to repeated internal conflicts from the period of the Northern and Southern Courts (Japan) to the Warring States period (Japan). The name of the clan originally was Uji, but the clan started to call themselves Aso during the generation of Koreyasu ASO.
The origin of the Aso clan, the daiguji of Aso-jinja Shrine having political ruling power, could date back to Korenobu ASO (Korenobu UJI) who lived in the early twelfth century according to records.
When the anti-shogunate movement by the Emperor Godaigo developed into the Genko War in 1333, which was in the late Kamakura period, Koretoki ASO received ryoji (an order) from the Imperial Prince Morinaga and cooperated with Takauji ASHIKAGA to attack Rokuhara Tandai (an administrative and judicial agency in Rokuhara, Kyoto).
Takauji then turned against the Kemmu Restoration which started after the Kamakura bakufu (Japanese feudal government headed by a shogun) fell. Koretoki ASO fought the Battle of Hakone and Takenoshita as busho (Japanese military commander) of the Emperor Godaigo's force, but was defeated. Then, Takauji was driven out from Kyoto to Kyushu as a result of the counter offensive by the Emperor Godaigo's forces, and in Kyushu, he was taken in by the Shoni clan. Korenao ASO, who was Koretoki's child, and the Kikuchi clan together fought against the troops formed by the Ashikaga and Shoni clans in the Battle of Tatarahama but they were defeated and killed themselves.
Period of the Northern and Southern Courts
Takauji again took over Kyoto causing the Emperor Godaigo to flee to Yoshino, and the period of the Northern and Southern Courts started. Koretoki ASO reassumed the role of head of the clan after Korenao died, but in the Northern Court, Magokumamaru SAKANASHI, an illegitimate child of Koretoki, was appointed to the head of the clan, causing the Aso clan to split. Magokumamaru was killed by Korezumi ASO (husband of Koretoki's daughter). However, the clan remained split because the family line including Koretoki, Korezumi, and Koremura ASO allied with the Northern Court, and the family line including Koretake ASO (younger brother of Koremura) allied with the Southern Court and fought against each other. The conflict was resolved when a great-grandson of Koretake, Koretoshi ASO, became an adopted son of a Koretada ASO, a grandson of Koremura. Later on, however, a fight over the position of the head of the clan started with Koretoshi ASO and his son Koreie opposing Koretada ASO and his son Korenori.
Period of Warring States and Onwards
After the Period of Warring States started, Korenori ASO won the Battle of Makunohira in 1484 and finally reunited the clan. The clan split yet again during the generation of the children of Korenori.
In 1507, Korenori's child, Korenaga ASO, took over the Kikuchi clan, which was shugo (military governor) of Higo Province (and called himself Taketsune KIKUCHI), and granted the position of daiguji to his younger brother, Koretoyo ASO. In 1513, however, Korenaga allied with the Shimazu clan, attacked Koretoyo, and drove him out to Hyuga Province. Korenaga appointed his legitimate son, Koresaki ASO, to daiguji and established a cloister government. In 1517, with the help of Chikanobu KAI who was the Hyuga local lord, Koretoyo counterattacked Korenaga and his son and regained the clan's home ground called Yabe Town.
With the support of Chikanobu KAI and his son Chikanao KAI (Soun), Koretoyo made the Aso clan prosper.
In 1523, Koretoyo lost control of Katashida-jo Castle to Korenaga and his son, and they even took over control of Kosa Town, Tomochi Town, and Nakayama; however, Koretoyo regained control over the castle in 1543, finally ending the internal conflicts that had continued for 30 years.
(Koresaki and his son Korekata ASO fled by themselves, turning to the Sagara clan, and the conflict officially ended in 1590 when Korekata swore loyalty to Koremitsu ASO.)
In 1549, Koretoyo offered 10,000 hiki (110,000,000 yen) as charges for repairing the Imperial Palace and was appointed to the Junior Second Rank by the Emperor Gonara.
Koretoyo tried to stabilize his territories by establishing an ally with the Otomo and Sagara clans. In 1578, during the generation of Koremasa ASO, however, when the Otomo clan was badly defeated by the Shimazu clan in the Battle of Mimi-kawa, local samurai lords in Higo allied with the Shimazu clan or Ryuzoji clan, which was an emerging clan at that time, to invade the territories of the Aso clan. Although Koremasa ASO barely retained the territories owing to excellent military strategies by the chief vassal, Soun KAI, the Sagara clan surrendered to the Shimazu clan in 1581, causing the Aso clan to be directly pressured by the Shimazu clan from the south.
In 1585 (or 1583), Soun KAI and his subordinate Soden TASHIRO died. Then, Koremasa ASO died in 1583, and Koretane ASO, who took over Koremasa's position, died in 1584. Because of the deaths of such powerful figures, the Aso clan quickly lost its power.
In 1585, the Aso forces were utterly destroyed as soon as the Shimazu troops entered Aso territories. The head of the family, Koremitsu ASO (Koretane's child), who was only two years old at that time, surrendered and ran away with his mother. This marked the fall of the Aso clan, the family of warlords. Koremitsu ASO later requested Hideyoshi TOYOTOMI who gained control over Kyushu to provide protection, was provided with a small territory, and was appointed to gunji of Aso-jinja Shrine, but he was deprived of all his daimyo privileges.
In 1593, Hideyoshi made Koremitsu kill himself on suspicion of allowing his vassals to involve themselves in Umekita ikki (uprising). However, after the Battle of Sekigahara, Kiyomasa KATO arranged provision of a territory to Koreyoshi ASO who was Koremitsu's younger brother and was appointed to daiguji of Aso-jinja Shrine that was revived by Kiyomasa. The Aso clan then continued throughout the Edo and Meiji periods, and in 1884, Koreatsu ASO, the head of the family at that time was baronized and the clan was raised to the peerage. See "Aso-jinja Shrine" edited by Koreyuki ASO (Gakuseisha, 2007) for further details.