Iza Nagi is a central character from the Dawn story arc of Phoenix. He lives in the mythical age of Japan during the latter part of the second century. Iza Nagi is the brother of Iza Nami, and the two are defined by a pivotal act of bravery; Iza Nagi saves the Phoenix's egg from a fire caused by molten lava. In gratitude for this act, the Phoenix grants the siblings a gift of its lifeblood, which bestows upon them an extraordinarily long lifespan of three thousand years.

Following this encounter, Iza Nagi, along with his sister Iza Nami, a baby Phoenix, and a group of animal companions including a monkey named Yota, a rabbit named Popo, and a tortoise named Noro, departs for the north in search of a new world. Upon arriving on an island, the siblings are revered by the local residents, who give Iza Nagi and his sister the divine name Amaterasu O-mikami, and they become the living gods of the tribe. This role places them at the center of the community's spiritual and daily life. The story introduces a significant conflict when Himiko, the Queen of the neighboring country Yamatai, hears a rumor about the Phoenix and orders her follower Sarutahiko to capture it, which inevitably draws Iza Nagi and the protected baby Phoenix into a larger struggle. His motivations stem from his protective actions toward the Phoenix egg and the subsequent journey to secure a safe existence for his group in a new land. His notable ability is the extended life granted by the Phoenix's blood.