Born in Shinano Province (Nagano Prefecture). He became lord of Nagano and also controlled territory in Totomi Province (Shizuoka Prefecture) and Hida Province (Gifu Prefecture). At first, he sided with Takauji Ashikaga, the chief opponent of the South Dynasty, but changed over to the South Dynasty Camp. Sadamune's family was traditionally one of the fine archers. Sadamune especially was distinguished.
He became lord of Nagano and also controlled territory in Totomi Province (Shizuoka Prefecture) and Hida Province (Gifu Prefecture). At first, he sided with Takauji Ashikaga, the chief opponent of the South Dynasty, but changed over to the South Dynasty Camp. He became a retainer of Yoshisada Nitta and attacked Takauji. He again switched sides and belonged to the Takauji Camp, attacked Yoshisada at Kanagasaki Castle (Fukui Prefecture) and then Akiie Kitabatake, another South Dynasty warrior, at Mino (Gifu Prefecture) when Akiie came there from a successful campaign at Ka makura. Sadamune was defeated by Akiie. He taught archery to Emperor Godaigo, who permitted him to attend the Court.
