Aso Koremasa served as a sengoku daimyō of Higo Province during the Sengoku and Azuchi-Momoyama periods. He was the high priest of the Aso Shrine in Higo.
In 1520, Koremasa was born as the son of Aso Koretoyo. He had the childhood name of Senjumaru.
In 1541, Mifune Fusayuki, the lord of Mifune Castle and a retainer of the Aso clan, colluded with the Shimazu clan of Satsuma Province to rebel against Koremasa’s father, Koretoyo. Upon orders of Koretoyo, Koremasa served as the general of a punitive force. With the support of Kai Sōun, Koremasa defeated the Mifune forces at the Battle of Kinokurabara and captured Mifune Castle in Mashikinokōri, compelling Fusayuki to take his own life.
In 1559, after the death of Koretoyo, Koremasa inherited the headship of the clan. Around this time, the Aso clan strained under pressure from the Shimazu of Satsuma and the Ryūzōji of Hizen Province. In a bid to maintain the independence of the clan, Koremasa relied upon Sōun to join forces with the Ōtomo of Bungo Province. Thereafter, he effectively collaborated with other powers to remain autonomous throughout his life.
In 1583, Koremasa died and was succeeded by his younger brother, Aso Koretane.