Hamamatsu Domain
Mizuno Tadakiyo was the eldest son of Mizuno Tadakuni, the "daimyō" of Hamamatsu Domain and chief senior councilor ("Rōjū") in service to the Tokugawa shogunate. After the failure of the Tenpō Reforms, Tadakuni was forced into retirement and exile, and turned the leadership of the Mizuno clan and the position of "daimyō" of Hamamatsu Domain to Tadakiyo in 1845.