Ashino Moriyasu served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was the sixteenth head of the Ashino clan based in Ashino in the Nasu District of Shimotsuke Province.

The Ashino were an illegitimate branch of the Nasu clan of Shimotsuke and counted among the Seven Clans of the Nasu.

Moriyasu was born as the eldest son of Ashino Sukeyasu (Yamato-no-kami), the fifteenth head of the Ashino clan.

In the third month of 1585, Moriyasu, together with his father, Sukeyasu, and lord, Nasu Sukeharu, confronted the allied forces of Shionoya Yoshitsuna and Utsunomiya Kunitsuna at the Battle of Usubagahara.  In this conflict, Moriyasu served in the vanguard of the Nasu forces which killed over 300 enemy troops en route to victory.  From the end of 1585 to the first month of 1586, when a dispute erupted between Iōno Sukenobu and Ōzeki Kiyomasu, Moriyasu sided with the Ōzeki (with which the clan had marital ties) and attacked Sukenobu.

In the seventh month of 1586, when the Nasu army assaulted the base of Shionoya Hōki-no-kami, Moriyasu served in the vanguard, destroying the gate as he fought his way into the castle.  In 1590, during the Conquest of Odawara, the Nasu were late deploying and, as result, removed from their position.  Moriyasu, however, participated in the expedition so he received official recognition of his rights to his landholdings which were limited to 800 koku.  That same year, during the Oushū Retribution by the Toyotomi administration, when members of the Toyotomi army stopped by his residence, Moriyasu prepared matcha, or green tea, to show hospitality toward the visitors.  Hideyoshi reciprocated by giving Moriyasu a short sword and gold pieces.  In 1592, members of the Nasu clan from the area all served in the Bunroku Campaign, perhaps at Nagoya Castle in Hizen Province which served as a logistics base in Japan for the war on the Korean Peninsula.

After the death of Toyotomi Hideyoshi in the eighth month of 1598, among the commanders of the Seven Clans of the Nasu, Moriyasu was the only one to receive a keepsake from Hideyoshi, a magoroku sword, reflecting that he was held in high regard by Hideyoshi.  Nevertheless, he did not receive an increase to his fief. 

Moriyasu died on 3/4 of Keichō 4 (1599) at the age of forty-four.  His lineal heir, Ashino Masayasu, succeeded him as head of the clan when he was only eight years old.