Lifespan: Unknown to 9/4 of Genki 2 (1571)
Title: Assistant Vice Minister of Academics
Clan: Mimura → Shō
Lord: Mōri Motonari
Father: Mimura Iechika
Adoptive Father: Shō Tamesuke or Hoida Sanechika
Siblings: Motosuke, Mimura Motochika, Mimura Motonori, Mimura Mototake, Mimura Mototaka, Ueda Sanechika, sister (wife of Ueno Takanori), sister (wife of Narasaki Motokane), Ryōjuin (formal wife of Mizuno Katsunari), sister (wife of Ishikawa Hisanori)
Shō Motosuke served as a bushō during the Sengoku period. Motosuke was the lord of Sarukake Castle in Bitchū Province. He was also known as Hoida Motosuke. There was a separate individual with the same name in the mid-fifteenth century who also served as the lord of Sarukake Castle.
Motosuke was born as the eldest son of Mimura Iechika, a daimyō in Bitchū.
The Shō clan served as deputy military governors of Bitchū, while the Hosokawa clan served as the military governors. However, as the power of the Hosokawa in Bitchū began to wane in the Sengoku period, kokujin, or provincial landowners, in Bitchū split between other regional powers including the Amago and Ōuchi clans and engaged in a power-struggle. Initially, the Shō clan and the Mimura clan joined forces to expand their influence, but, in 1559, at the Battle of Sarukake, the two clans came into conflict. Their differences could not easily be resolved, so, upon request of Mimura Iechika, the Mōri clan finally mediated a settlement. As a result, Motosuke was adopted (either by Shō Tamesuke or Shō Sanechika) as the designated heir of the Shō clan.
Service to the Mōri clan
As his adoption by the Shō clan, he adopted the name of Motosuke comprised of the character “moto” used in the Mōri clan and the character of “suke” used for generations in the Shō clan. He also changed his personal seal. As a cadet family of the Mimura, and under the command of the Mōri, Motosuke served loyally.
In 1567, at the Battle of Myōzenji, Motosuke served as commander of the right wing of the Mimura army in a battle to revenge for the assassination of Mimura Iechika by Ukita Naoie. Motosuke incurred a bitter defeat in this battle. Thereafter, however, under the command of the Mōri, he led kokujin from Bitchū on deployments in Kyūshū and other locations. The Mōri praised his contributions on the battlefield.
There are several theories concerning the demise of Motosuke. According to accounts from the period, he was killed in action while serving in a rear guard against the Uragami and Ukita forces in a battle for Saita Castle in Bitchū. This occurred on 9/4 of Genki 2 (1571). Under another theory drawing from accounts of descendants of the Mimura clan and genealogies, during the Bitchū Conflict in 1575, he allied with the Bitchū-Mimura clan (his original family) to fight against the Mōri, dying at Saita Castle. Finally, there are materials from the Mōri family indicating that he died in the first month of 1571 at Saita Castle in fighting against Ukita forces.
According to genealogies of the Mōri clan created in later years, Motosuke was adopted by the fourth son of Mōri Motonari (Mōri Motokiyo, also known as Hoida Motokiyo), but, in a letter written by Motokiyo himself, he adopted the surname of Hoida from the Hoida neighborhood where he resided in Sarukake Castle, refuting a relationship with the Shō clan.