Lifespan: Eishō 9 (1512) to 6/12 of Genki 2 (1571)
Clan: Hongō → Shimazu-Hōshū family
Father: Hongō Tadasuke
Mother: Daughter of Shimazu Tadakado
Adoptive Father: Shimazu Tadahiro
Siblings: Tadachika, sister (wife of Itō Sukemitsu), Tadataka, sister, Hisaie
Wife: [Formal] Daughter of Nejime Sonchō
Children: Hongō Tokihisa, Hisamichi, Shimazu Tomohisa
Shimazu Tadachika served as a bushō in Hyūga and Satsuma Provinces during the Sengoku period. He was the ninth head of the Hongō clan and the fifth head of the Hōshū family, a cadet family of the Shimazu clan, the shugo daimyō of Satsuma Province in Kyūshū.
In 1512, Tadachika was born as the eldest son of Hongō Tadasuke, the landlord of Miyakonojō in Hyūga Province.
In 1546, Shimazu Yoshihisa, the adopted son of Shimazu Tadahiro of the Hōshū family, died early, so Tadachika had his eldest son, Hongō Tokihisa, inherit the Hongō clan while Tadachika entered the Hōshū family as an adoptee. In 1549, he inherited the family following the retirement of his adoptive father.
For generations, the Hōshū family incurred attacks from the Itō clan of Hyūga. Tadachika withstood continuing aggression but the strength of the Itō gradually increased. In 1560, Tadachika adopted Shimazu Yoshihiro (the second son of Shimazu Takahisa, the fifteenth head of the main branch of the Shimazu clan) who was known as an intrepid warrior and assigned him to guard Obi Castle in the Minami District of Hyūga. In 1562, upon orders of Takahisa, Yoshihiro, after Yoshiro left Obi Castle, Itō Yoshisuke attacked the castle. Tadachika settled with Yoshisuke, and, initially turned-over the castle, but, several months later, recovered the castle in a nighttime attack. In 1568, Yoshisuke led 20,000 soldiers to attack again, and, after repelling reinforcements from the main branch of the Shimazu clan along the way, laid siege to the castle. After the besieging forces cut supply lines to the castle, the main branch of the Shimazu clan made a decision to abandon the site, whereupon Tadachika fled and the castle fell to the Itō army.
Following the fall of Obi Castle, Tadachika moved to Miyakonojō and, in 1571, died of illness in this location at the age of sixty-eight.