Lord of the Kikkawa and one of the 'Two Rivers'.

At the age of 20, Motoharu, Môri Motonari's 2nd son, became the head of the Kikkawa daimyo family of Aki. In 1550 Motonari arranged for a son to be adopted and named as heir by the Kikkawa house. The previous lord, Okitsune, had been a rival of the Mori and had allied himself with the Amako in the 1540's. Motonari had responded by pressuring Okitsune to adopt his son Motoharu; in 1550 Okitsune was forced into retirement and succeded by Motoharu (Okitsune was later killed on Môri's orders). The Kikkawa became vassals to the Môri but maintained an important presence into the Edo Period. Motoharu proved himself an invaluable asset to his father and a warrior of great skill. He served at the Battle of Miyajima (1555), the Gassan - Toda Campaigns (1563-66), the sieges and counter-sieges of Moji and Matsuyama Castles (Buzen province, 1557-1563), the Battle of Torisaka (Iyo province, 1568), and countless other, less-notable engagements. Many of these actions saw Motoharu fighting side by side with his brother Kobayakawa Takakage, and popular conception has Motoharu the brawn to Takakage's brains.

After Gassan - Toda and the later death of Motonari, Motoharu became the guardian of Izumo and Hôki (taking up residence in Gassan-Toda Castle) and clashed with the Amako-loyalist Yamanaka Shikanosuke. Motoharu was active in the war with the Oda that culminated in the Siege of Takamatsu Castle in Bingo. After the death of Oda Nobunaga (1582) played important role in Toyotomi Hideyoshi's conquest of Shikoku in 1585, landing with his brother Kobayakawa on Iyo with 30,000 men. He died the next year, followed in 1587 by his son Motonaga (1547-1587). Motoharu was considered a splendid leader of men and, along with his brother Takakage, a pillar of the Môri clan.