Lord Hosokawa Incident
The Lord Hosokawa Incident (Hosokawa-dono no hen) occurred on 6/23 of Eishō 4 (1507). This refers to the assassination of Hosokawa Masamoto, the kanrei, or deputy shōgun, of the Muromachi bakufu. Masamoto further served as a bushō and shugo daimyō of Tanba, Settsu, and Tosa provinces, and as the twelfth head of the Hosokowa-Keichō family – the main branch of the Hosokawa clan. Masamoto ousted Ashikaga Yoshiki (later known as Yoshitada and Yoshitane) from his role as the tenth shōgun, replacing him with Ashikaga Yoshitō (later known as Yoshitaka and then Yoshizumi) and himself becoming the de facto ruler. This gave rise to him being called the “half shōgun.” Owing to the absence of a natural heir, Masamoto’s assassination led to a prolonged and bitter succession struggle between his adopted sons vying for control of the Hosokawa clan as well as the Muromachi bakufu under members of the ruling Ashikaga family backed by the respective sides to the conflict. The event of his assassination is known as the Lord Hosokawa Incident and the broader succession struggle as the Eishō Disturbance (Eishō no sakuran), named after the Eishō era during which it occurred.
In 1507, Masamoto expanded the reach of the Hosokawa clan by providing support to Takeda Motonobu of Wakasa Province, having two of his adopted sons, Hosokawa Sumiyuki and Hosokawa Sumimoto, attack the base of Isshiki Yoshiari in Tango Province. However, Masamoto apparently grew battle-weary, indicating a desire to travel around Mutsu Province and engage in ascetic practices as an adherent of shugendō. Masamoto gave up this plan after being remonstrated by his retainer, Miyoshi Yukinaga. In the midst of attacking Isshi Yoshiari to support Takeda Motonobu, Masamoto complied with an Imperial edict to return to Kyōto.
Masamoto immersed himself in shugendō, frequently acting eccentrically and portraying himself as Tengu, a mythological creature in the view of believers. On 6/23 of 1507, while entering the bathroom in the residence in preparation to practice sorcery, he was murdered by a secretary from the Tokura clan upon the urging of retainers who supported one of his adopted sons, Hosokawa Sumiyuki, including Yakushiji Nagatada, Kōzai Motonaga, and Takeda Magoshichi (a member of Masamoto’s security detail). The day after the incident, Nagatada led an attack against the residences of another adopted son, Hosokawa Sumimoto, and Miyoshi Yukinaga, forcing Sumimoto and Yukinaga to flee to Ōmi Province, and supported Sumiyuki as the successor to the Hosokawa-Keichō family. On 6/26, Akazawa Tomotsune, who, upon earlier orders of Masamoto, was attacking Isshiki Yoshiari of Tango Province, attempted to have his army retreat to Kyōto, but was forced to kill himself after being subject to a counterattack by Yoshiari and Ishikawa Naotsune, a kokujin, or provincial landowner, from Tango. Tomotsune’s adopted son, Akazawa Nagatsune, escaped safely and came under the command of Sumimoto.
One more of the adopted sons, Hosokawa Takakuni, consulted with Hosokawa Masakata (a district-level shugo, or military governor, in Settsu Province), Hosokawa Hisaharu (the military governor of Awaji Province), and Hatakeyama Yoshihide (the military governor of Kawachi Province), and agreed to have Sumimoto become the successor to Masamoto. On 7/28, Yakushiji Kuninaga (the son of Yakushiji Motokazu who had earlier been killed by Motokazu’s younger brother, Yakushiji Nagatada), captured Nagatada’s home base at Ibaraki Castle. The next day, Takakuni captured Kōzai Motonaga’s home base of Arashiyama Castle. On 8/1, Miyoshi Yukinaga and kokujin from the Kōka District of Ōmi to where he had earlier fled quickly returned to Kyōto, and together with the forces under Takakuni, attacked and toppled the last residence held by Sumiyuki known as Yūshoken in Kyōto, causing Sumiyuki to take his own life. The day after, Sumimoto met the shōgun, and inherited the Hosokawa-Keichō family.
Reasons for the assassination
Kōzai Motonaga is viewed as the ringleader of the assassination. Although Masamoto originally adopted Sumiyuki to be his designated heir, he may have gradually come to regret the promise owing to deep opposition within the family toward the prospect of an unrelated person becoming his successor, whereupon he accepted Sumimoto from the branch of the Hosokawa in Awa Province instead. This, however, resulted in a loss of authority for Motonaga, who had been serving as Sumiyuki’s assistant. Meanwhile, Masamoto had assigned a retainer of the Keichō family named Miyoshi Yukinaga to serve as Sumimoto’s assistant. Masamoto increasingly relied upon Yukinaga for his military prowess and also made him the new chief of staff, significantly expanding his authority within the Hosokawa clan. Yukinaga moved from Awa to serve Sumiyuki while continuing to have a role in governing Sanuki Province in Shikoku. Sanuki was also Motonaga’s birthplace, fueling resentment toward Yukinaga. Moreover, Masamoto’s inclination to generate a lot of problems made family members worried about their future, causing the retainers to support Sumiyuki and assassinate Masamoto as a means to seize power.
Sumiyuki himself may have been working behind the scenes. In 1506, soon after his coming-of-age ceremony and removal from the line of succession, he obeyed orders from Masamoto to attack Kaetsu en route to subjugate Isshiki Yoshiari in Tango Province. These actions were for appearances only, while, in fact, Sumiyuki conspired with the Isshiki to feign capture of the castle and then withdraw his forces. Ishikawa Naotsune of Kaetsu Castle that Sumiyuki earlier pretended to capture successfully attacked Akazawa Tomotsune at the time that Tomotsune attempted to lead his forces back to Kyōto following news of Masamoto’s assassination. Sumiyuki conspired with others prior to these events which appear to have been meticulously planned. Resentment at the revocation of his appointment as Masamoto’s designated successor was likely the primary motive for his actions.