Reia is introduced as a member of the church who arrives at the Swan after being attacked by Ran's bandit thugs, presumably to keep an eye on Kenshi on behalf of the church. She becomes interested in Kenshi's family after he tells her that his mother is also named Reia.
After arriving at the barrier workshop, Reia steals an item that is supposed to help stop Gaia, and reveals herself to be Neizai. As Ulyte sometimes transforms into Reia, he dons the disguise of Neizai whenever he switches bodies, so that no one knows of Reia's existence, or the fact that he and Reia are in the same body. In the last episode, when Ulyte's body finally fails him for good, Reia takes over permenantly.