Tokugawa Ieshige
Masaharu was the second son of Yonekura Masanori, a 3000 "koku" "hatamoto". He was adopted as head of the Yonekura clan and on the unexpected death of Yonekura Satonori without any heirs in 1749. He was confirmed as "daimyō" of Mutsuura Domain in a formal audience with "Shōgun" Tokugawa Ieshige.