Harumoto was the son of Hosokawa Sumimoto. Following the defeat and suicide of Hosokawa Takakuni, Harumoto assumed the rank of kanrei and chose to retain Ashikaga Yoshiharu as shôgun. Harumoto found himself challenged by Miyoshi Motonaga of Settsu province, a growing power and the head of a family that had drawn away from the Hosokawa in recent years. Though Miyoshi was a formidable opponent, Harumoto allied with the warlike monks of the Ishiyama Honganji and managed to trap Motonaga and force him to commit suicide (1532). Despite Motonaga's demise, the Miyoshi clan continued to harass Harumoto, growing in strength even as the Hosokawa weakened. In addition, the Hosokawa and Honganji parted ways soon after Motonaga's death and Harumoto attacked the Ishiyama Honganji in 1533. Harumoto's greatest rival proved to be Miyoshi Nagayoshi (otherwise known as Miyoshi Chokei), Motonaga's son and a gifted schemer and politician. He was also forced to battle a relative, his cousin Hosokawa Ujitsuna, who was envious of his position. In 1545 shôgun Ashikaga Yoshitane fled Kyoto, abdicating in favor of his son Yoshiteru. Harumoto shifted his allegiance to Yoshiteru but began to lose his influence with the young shôgun through the activities of the Miyoshi. Miyoshi Nagayoshi and Matsunaga Hisahide convinced Yoshiteru to distance himself from Harumoto, and in 1549 the latter was forced to flee the capital. Harumoto continued to fight with the Miyoshi, and in August 1553 he attacked Kyoto and burned much of it. He next attempted unsuccessfully to convince Ashikaga Yoshiharu to come out of retirement. He was finally captured by Chokei in 1559 but was allowed to retire to a temple (albeit under guard) in Settsu and died four years later. A man of some military accomplishment, Harumoto was said to have been an early proponent of the use of firearms.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005