The risen empire / Westerfeld, Scott

The undead Emperor, having ruled for over one thousand years supported by the Risen, an elite group he has granted eternal life, finds his empire of eighty worlds threatened when the Rix, machine-augmented humans who seek to make all minds one through Artificial Intelligence, kidnap the tyrannical Emperor's sister, the eternal Child Empress.

The undead Emperor has ruled his mighty interstellar empire of eighty human worlds for sixteen hundred years. Because he can grant a form of eternal life, creating an elite known as the Risen, his power has been absolute. He and his sister, the Child Empress, who is eternally a little girl, are worshiped as living gods. No one can touch them. Not until the Rix, machine-augmented humans who worship very different gods: AI compound minds of planetary extent. The Rix are cool, relentless fanatics, and their only goal is to propagate such AIs throughout the galaxy. They seek to end, by any means necessary, the Emperor's prolonged tyranny of one and supplant it with an eternal cybernetic dynasty of their own. They begin by taking the Child Empress hostage. Captain Laurent Zai of the Imperial Frigate Lynx is tasked with her rescue. Separated by light-years, bound by an unlikely love, Zai and pacifist senator Nara Oxham must each in their own way, face the challenge of the Rix, and they each will hold the fate of the empire in their hands.

Zai and pacifist senator Nara Oxham challenge the Rix, machine-augmented people who worship planet-sized beings with artificial intelligence and seek to supplant the power of the undead Emperor and his sister, the Child Empress, who have ruled for sixteen hundred years.