Lifespan: Kakitsu 1 (1441) to 11/11 of Meiō 9 (1500)
Other Names: Izaku Hisayasu
Clan: Shimazu → Shimazu-Izaku
Father: Shimazu Tadakuni
Adoptive Father: Shimazu Norihisa
Siblings: Tomohisa, Tatsuhisa, Hisayasu, Katsuhisa, Tadatsune, Morimune, Tadahiro, Yorihisa, sister (wife of Ijūin Hirohisa), Inuyasumaru (adopted brother)
Shimazu Hisayasu served as a bushō during the early Sengoku period. He served as the eighth head of the Shimazu-Izaku, a cadet family of the Shimazu clan of Satsuma Province.
In 1441, Hisayasu was born as the third son of Shimazu Tadakuni, the ninth head of the Shimazu clan.
In 1458, Inuyasumaru, the seventh head of the Shimazu-Izaku family, suddenly died at a young age so Hisayasu was adopted and inherited the headship of the family. The Shimazu-Izaku became a cadet family from an early time in the Kamakura period so had a distant relationship with the main branch of the Shimazu clan. Although the Shimazu-Izaku were relatives of the main branch, their status was that of retainers.
In 1473, upon orders of Shimazu Tatsuhisa (the tenth head of the Shimazu clan, a shugo daimyō, and the military governor of Satsuma, Ōsumi, and Hyūga provinces), Hisayasu prepared defenses against the Itō clan in Kushima in Hyūga. After the death in 1474 of Tatsuhisa, the Niiro clan, a powerful opposing cadet family, made a request to Shimazu Tadamasa, the eleventh head of the Shimazu clan who succeeded Tatsuhisa, to return Hisayasu to the Shimazu-Izaku family, and Tadamasa consented to their request. Rejecting this plan, Hisayasu plead for support from the Itō clan of Hyūga and the Ōtomo clan of Bungo Province and attacked the Niiro clan at Obi Castle, revolting against Tadamasa. As Hisayasu and his allied forces approached the base of Tadamasa at Shimizu Castle in Kagoshima, Tadamasa had his wife and children take refuge in Ichiuji Castle in Ijūin. In 1484, however, Tadamasa led relatives including Shimazu Tomohisa of the Shimazu-Sōshū (a cadet family) and Shimazu Kunihisa of the Shimazu-Sasshū family on a deployment to subdue the Shimazu-Izaku family. After suffering a defeat at Sueyoshi, Hisayasu retreated to Kushima. That same year, he surrendered and returned to Izaku.
Thereafter, in 1494, his lineal son, Shimazu Yoshihisa, was murdered by a manservant, whereupon Hisayasu himself got swept-up in the internal conflict in the Shimazu-Sasshū family. In 1500, he incurrred an attack by Shimazu Tadaoki of the Sasshū family and was killed in battle. He was sixty years old.