Sadayuki was the son of [[Usami Takatada]] and was long a notable retainer of the [[Nagao clan|Nagao]] of [[Echigo province]]. He helped convince the young [[Uesugi Kenshin]] (then known as Nagao Kagetora) to rebel against his elder brother [[Nagao Harukage|Harukage]] and led troops for him during the resulting civil war. In [[1564]] he is reputed to have murdered [[Nagao Masakage]] on Kenshin's orders, though given that he himself appears to have died (of drowning) during the same incident makes this somewhat odd. According to one story, Masakage's son, [[Uesugi Kagekatsu|Kagekatsu]], held a resentment against the [[Usami clan|Usami]] for this, and when he assumed command of the Uesugi in [[1579]], compelled Sadayuki's son [[Usami Katsuyuki|Katsuyuki]] to flee Echigo.
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Sadayuki, also known as Sadamitsu, was for years one of [[Uesugi Kenshin|Uesugi Kenshin's]] chief retainers, having supported him in his war for control of [[Echigo province|Echigo]].
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The son of [[Usami Takatada]], he was long a notable retainer of the [[Nagao clan]] of Echigo. He helped convince the young Uesugi Kenshin (then known as Nagao Kagetora) to rebel against his elder brother [[Nagao Harukage|Harukage]] and led troops for him during the resulting civil war. In [[1564]] he is reputed to have murdered [[Nagao Masakage]] on Kenshin's orders, though given that he himself appears to have died (of drowning) during the same incident makes this somewhat odd. According to one story, Masakage's son, [[Uesugi Kagekatsu|Kagekatsu]], held a resentment against the [[Usami clan|Usami]] for this, and when he assumed command of the Uesugi in [[1579]], compelled Sadayuki's son [[Usami Katsuyuki|Katsuyuki]] to flee Echigo.