Traditionally said to have been born around 1118 (though his exact dates are debated), Yuasa Munesige was a warrior based in Arida District, Kii Province. In 1143 he moved his base from Hiroyasu Mountain Castle and built Yuasa Castle in the Yuasa estate. In 1159, while Taira no Kiyomori was on a pilgrimage to Kumano, Munesige brought him urgent word of the Heiji Rebellion and accompanied him to the capital, afterward rising to prominence as a leading warrior on the Taira side. After the fall of the Taira, he held out at Yuasa Castle in support of Tadafusa, son of Taira no Shigemori, but surrendered to Minamoto no Yoritomo in 1186 and had his lands confirmed. He then expanded his influence from Yuasa Castle by placing his sons throughout Arida District, laying the foundation of the warrior band known as the Yuasa-to (Yuasa clan). He is also said to have been a devout patron of shrines and temples, funding their repair and construction. He is believed to have died around 1195. The Buddhist monk Myoe, founder of Kozan-ji temple, was his grandson.

A skilled warrior who also possessed sharp political instincts, navigating the turbulent shift of allegiance from the Taira to the Minamoto. He was also known for his deep religious devotion.

The Yuasa Castle Munesige built remained the seat of the Yuasa clan for generations and was renowned as a formidable stronghold, repelling three assaults by the Hatakeyama clan in 1447 before finally falling. The castle ruins were designated a National Historic Site in 2021 as the "Yuasa-to Castle Remains."