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Born in Tajihi, Aki province, Takamoto was sent at the age of 14 to Suo province as a hostage of Ōuchi Yoshitaka. This was done to ensure his father's loyalties to Ōuchi. He was allowed to return home in 1540, three years later, to the Mōri castle of Yoshida Kōriyama.
In 1555, Sue Harukata, one of Ōuchi's vassals, staged a coup and forced Ōuchi Yoshitaka to commit suicide. He was then attacked by Mōri Takamoto and his father, and was defeated in the battle of Miyajima. The Mōri, defeating the Sue/Ōuchi forces, thus rose to power in the Chūgoku region (the western area of Honshū), and would remain a powerful and influential faction for much of the rest of the 16th century. Upon his father's retirement two years later, Takamoto inherited formal leadership of the family, but his father Motonari continued to wield actual control over the clan's affairs.
When Ōuchi Yoshinaga died that same year (1557), the Mōri saw an opportunity to seize the Ōuchi clan lands; they had to consider, however, the Ōtomo clan to the west and the Amago clan to the north who entertained similar ideas. Takamoto gained a considerable boost to his power, however, in 1560-1563, when he was appointed by Shogun Ashikaga Yoshiteru as Governor (shugo) of Aki, Nagato, Suo and Bitchū provinces. Amago Haruhisa died suddenly in 1560, and Ōtomo Sōrin began to devote significant resources to attacking the Amago territory.
At the advice or orders of his father, Takamoto seized the opportunity to attack the Ōuchi territory. He was leading the Mōri armies through Bingo province when, on the 18th day of the 9th month of 1563, he suddenly died of poisoned food at the age of 41. Historians have since identified Wachi Saneharu, a local Bingo samurai, of committing the deed.
Mōri Motonari accused a number of samurai of conspiring in the assassination, and forced them to commit seppuku. Takamoto's son Mōri Terumoto was selected as his heir, but Motonari continued to wield the true power.
- Father: Mōri Motonari (1497–1571)
- Son: Mōri Terumoto(1553–1625)
- This article is derived from the corresponding one on the Japanese Wikipedia.