Minami Nagayoshi served as a bushō in Mutsu Province during the Sengoku period.

In 1507, Nagayoshi was born as the third son of Nanbu Masayasu.  (There is also a theory that he was the son of Nanbu Yasunobu.) 

In 1524, after Sandai Mondo from the Tsugaru region launched a rebellion, Nagayoshi became the lord of Asamizu Castle in the Sannohe District of Mutsu Province.  He initially adopted the surname of the Asamizu clan with a fief in Gonohe and Asamizu.

Thereafter, he served valorously in the military and received a fief of 3,500 koku.  As an important retainer of the Nanbu family, Nagayoshi participated in the council held after the death of Nanbu Harutsugu to determine the successor as the next head of the Nanbu clan.  During internal conflicts in the Nanbu clan from 1558 to 1570, Nagayoshi joined the faction supporting Nanbu Nobunao so he incurred an attack by Nanbu Harumasa.

Nagayoshi’s residence stood to the south of Sannohe Castle so was called Minami-den, or South Mansion.  He adopted the surname of Minami based on the name of his residence. 

In 1591, during the Revolt of Kunohe Masazane, Minami Moriyoshi (Nagayoshi’s grandson) from the third generation of the Minami clan was attacked by the Kushibiki clan but repelled them, forcing them to flee in defeat.  Moriyoshi, however, chased them too far, and was killed in the environs of the Hōshioka mansion.  He was succeeded by his younger brother, Minami Naoyoshi.

The Minami clan continued to serve the Nanbu clan for over one-hundred years.