Niiro Tadazumi served as a bushi during the Sengoku period.  He was a grandson of Niiro Korehisa.

Tadazumi was born as the son of Niiro Tomoyoshi of an illegitimate branch of the Niiro clan.

He entered the priesthood, adopting the monk’s name of Gyoin.  Upon request of his aunt, Shimazu Tokiwa, he provided instruction to her son, Kikusaburō (later known as Shimazu Tadayoshi), in the subjects of Buddhism, Confucianism, and political affairs.  When the main branch of the Niiro clan based in Shibushi dissipated, he introduced Tadayoshi to Niiro Sukehisa, Tadazumi’s nephew from the same illegitimate branch of the clan.  Sukehisa was the father of Niiro Tadamoto.