So Sadakuni was a Japanese warrior. Lord of Tsushima Island.
So Sadakuni was born in 1422. He was the second son of Morikuni.
In 1469, he and Yoritada Muto, who had come to Tsushima to ask for his protection, fought Masahiro Ouchi and defeated him. Sadakuni recovered his former territory in Chikuzen (Fukuoka Prefecture) as a result of this battle. He made Ilakata his stronghold in Kyushu. Later the ouchis became powerful again and took Sadakuni's territory in Kyushu, making him only the Lord of Tsushima.