Lifespan: 5/23 of Tenbun 6 (1537) to 4/15 of Kōji 3 (1557)
Other Names: Chiyonabemaru (childhood); Tarō, Suketarō (common)
Father: Kabayama Yoshihisa
Mother: Osumi (second daughter of Shimazu Tadayoshi, older sister of Shimazu Takahisa)
Kabayama Tadasoe served as a bushō during the Sengoku period. He was a retainer of the Shimazu clan of Satsuma Province.
The Kabayama were an illegitimate branch of the Shimazu clan. The Kabayama were founded by Shimazu Sukehisa, the fifth son of Shimazu Tadamune, the fourth head of the Shimazu who served as the military governors of Satsuma Province. Sukehisa first acquired landholdings in Kabayama, Hayamizu, and Terabashira in the Mimata-in manor in Hyūga Province.
In 1537, Tadasoe was born as the lineal heir of Kabayama Yoshihisa, the eighth head of the Kabayama clan.
In 1550, Tadasoe attended his coming-of-age ceremony during which his grandfather, Shimazu Tadayoshi, crowned him with an eboshi, or black-lacquered hat, to mark the celebration. In 1554, Tadasoe served in a siege of Iwatsurugi Castle in Hiramatsu in Satsuma. In 1557, during battles against the Gamō and Hishikari clans, an event known as the Battle of Tentō, he sustained injuries while attacking the enemy camp and died later that day from the injuries. He was twenty-one years old.
To mourn the loss, Shimazu Yoshihisa composed a waka, or traditional poem. It is noted in the prelude to the poem that Yoshihisa deeply lamented the death of Tadasoe at Kokubu/Nagahama Castle in Ōsumi Province in Kōji 3 (1557) from serious injuries sustained after being struck with a sword by Hishikari Shigetoyo while attacking the Gamō in battle.
After his death, his mother, Osumi, entered the priesthood to incessantly chant Buddhist mantras for his soul.