Motochika was the son of Mimura Kii no kami Iechika. His domain lay in Bitchû province His father was assassinated in 1566 this was suspected to have been arranged by his rival Ukita Hideie. Motochika was forced to call on the assistance of the Môri when his domain was threatened by former Amako retainers under Yamanaka Shikanosuke. He later entered into secret communications with the Oda which, unfortunately, came to the attention of the Môri and made them enemies. Motochika found himself assailed by an overwhelming Môri army in 1575 and lost his Matsuyama castle to Kobayakawa Takakage. He escaped the castle at the last minute but was injured in the effort, afterwards committing suicide.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005