Mimura Motonori served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Mimura clan and lord of Yuzuriwa Castle in Bitchū Province.

Motonori was born in 1549 as the third son of Mimura Iechika.  After the death of Iechika, he served as an assistant to his older brother, Mimura Motochika, who became the successor to Iechika as the head of the clan.  Motochika allied with Oda Nobunaga and abandoned Mōri Motonari during the Bitchū Conflict (Bitchū hyōran).  While holed-up in Yuzuriwa Castle, Motonori was attacked by Mōri forces led by Kobayakawa Takakage.  An expert with the long sword, Motonori fought valiantly but, in the end, was subject to an honorable death in battle.  He was twenty-seven years old.

Based on a letter of commendation from Mōri Terumoto to Narasaki Toyokage dated in late 1574, Yuzuriwa Castle was likely toppled before the Bitchū Conflict in 1575.