Lifespan: Entoku 1 (1489) to 8/1 of Eishō 4 (1507)
Clan: Kujō → Hosokawa-Keichō (main branch of the Hosokawa family)
Bakufu: Muromachi – kanrei (deputy shōgun)
Lord: Ashikaga Yoshizumi (the eleventh shōgun)
Father: Kujō Masamoto
Adoptive Father: Hosokawa Masamoto
Mother: Daughter of Musha-no-koji Takamitsu
Siblings: Kujō Hisatsune, Sumiyuki
Hosokawa Sumiyuki served as a bushō during the late Muromachi and Sengoku periods. He was the twenty-ninth kanrei, or deputy shōgun, of the Muromachi bakufu and the thirteenth head of the Hosokawa-Keichō family. His temporary ascension to these roles followed in the wake of the assassination of his adoptive father, Hosokawa Masamoto, which, in turn, led to his own demise less than two months later.
In 1489, Sumiyuki was born as the last son of Kujō Masamoto, the kanpaku, or Chief Advisor to the Emperor. His mother was the daughter of Musha-no-koji Takamitsu. Masamoto was succeeded by Kujō Hisatsune, Sumiyuki’s brother of a different mother who was twenty years older than him.
On 2/13 of Entoku 3 (1491), at the age of two, Sumiyuki was adopted by Hosokawa Masamoto who was single, had no natural children, and served as the twenty-fourth, twenty-sixth, twenty-seventh, and twenty-eighth deputy shōgun). He adopted the name of Sōmeimaru which had been used for generations of heirs to the Hosokawa-Keichō family – the main branch of the Hosokawa based in Kyōto.
In the ninth month of 1502, his adoptive father, Masamoto, formally designated Sumiyuki as his heir (successor to the family) and awarded him the role of military governor of Tanba Province. Masamoto and Sōmeimaru, however, did not get along well together, so, in the fifth month of 1503, Masamoto removed him from the line of succession and newly appointed as his heir another adoptee, the son of Hosokawa Yoshiharu from the branch of the Hosokawa family serving as the military governors of Awa Province in Shikoku. He was named Rokurō and later became known as Hosokawa Sumimoto.
In 1504, Sōmeimaru attended his coming-of-age ceremony and received one of the characters in his name from a cousin on his mother’s side, Ashikaga Yoshizumi, the eleventh shōgun of the Muromachi bakufu, and adopted the name of Sumiyuki. Originally, the second character in the real name of the designated heir of the Hosokawa-Keichō family was “moto,” but this was already assigned to Rokurō who received the name of Sumimoto at his coming-of-age ceremony as the adopted heir to the family. Meanwhile, the character “yuki” was not used by successors to the family with the only exceptions being Hosokawa Yoriyuki (the first head of family) and Hosokawa Mochiyuki (a successor to his older brother, Hosokawa Mochimoto, and grandfather of Masamoto). Therefore, based on the adoption of the name Sumiyuki for Sōmeimaru, it is clear that, prior to his coming-of-age ceremony, he was not the designated heir to the family.
In 1506, Sumiyuki followed orders from Masamoto to subjugate Isshiki Yoshiari in Tango Province and he attacked Kaetsu Castle, but he the colluded with the enemy to pretend that the castle was captured and withdrew his forces. Not appearing to take offense to his removal from the line of succession, Sumiyuki’s obedience the orders of his adoptive father was only for the sake of appearances.
In the sixth month of 1507, servants of Masamoto who supported Sumiyuki as the successor, namely, Kōzai Motonaga and Yakushiji Nagatada, devised a plot to assassinate Masamoto as a means to seize the authority to back Sumiyuki as the successor. 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 Motonaga, Nagatada, and Takeda Magoshichi (a member of Masamoto’s security detail). The day after the incident, Nagatada led an attack against the residences of Sumimoto and Miyoshi Yukinaga (the kasai, or head of house affairs), forcing Sumimoto and Yukinaga to flee to Ōmi Province, and supported Sumiyuki as the successor to the Hosokawa-Keichō family. The killing of Masamoto is known as the Lord Hosokawa Incident which occurred in the context of the broader succession struggle known as the Eishō Disturbance.
After being met by Motonaga and others, Sumiyuki went from Tanba to Kyōto, held a memorial service for Masamoto, and was recognized by Ashikaga Yoshizumi (the shōgun) as the successor to the Hosokawa-Keichō family. Servants of the Hosokawa-Keichō family led by Motonaga and Nagatada performed a primary role by backing Sumiyuki as the head of the Hosokawa-Keichō family as a means to eliminate the influence of Miyoshi Yukinaga and others in his home province of Awa. However, Ishikawa Naotsune of Kaetsu Castle (who earlier colluded with Sumiyuki to pretend that the castle had fallen) launched an all-out attack on Akazawa Tomotsune during a siege by the Akazawa forces of the Isshiki clan, killing Tomotsune. This indicated that Sumiyuki was a participant in the meticulously planned assassination of Masamoto with the primary motivation most likely resentment over his removal from the line of succession to the Hosokawa-Keichō family.
After Sumiyuki and Sumimoto, prior to his demise, Masamoto had adopted a third son – Hosokawa Takakuni. Takakuni gained support among the members of the Hosokawa family, and, after bringing in the Hatakeyama clan from Takaya Castle, succeeded in rallying to his side the powers in the Kinai region. From their temporary refuge in Ōmi Province, Sumimoto and Miyoshi Yukinaga garnered support from kokujin, or provincial landowners, in Ōmi and, on 8/1, despite being late to the cause, launched an attack in Kyōto. In the course of this battle, Sumiyuki lost his primary general, Ichinomiya Hyōgo-no-suke. With no prospect for victory, Sumiyuki took his own life in his residence, dying at the age of nineteen. Meanwhile, Motonaga (after being struck by by a stray arrow) and Nagatada were both killed in action so, after a term of only forty days, Sumiyuki’s administration came to an abrupt end.