Sadamitsu was for years one of Uesugi Kenshin's chief retainers, having supported him in his war for control of Echigo. He drowned in 1564, apparently in the process of murdering Nagao Masakage on Kenshin's orders.
References
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005