After defeating an alien species called the Usurpers with combat androids known as Neans, humanity colonized Mars and enjoyed a period of post-war peace. With their role as soldiers complete, the Neans became subservient laborers and second-class citizens under human rule. Because they require a daily dose of Nectar to survive, the androids rely on their masters for this drug. Within this social hierarchy exist Proto-Neans, independent specialized androids capable of summoning metallic exoskeletons with superhuman abilities. Rouge Redstar is one such Proto-Nean, working undercover for Aletheia, the government agency that regulates Neans, alongside her human partner, Naomi Orthmann. Rouge and Naomi are tasked with eliminating the Immortal Nine—Proto-Neans who pose a threat to humanity for cryptic reasons. Meanwhile, an investigator is traveling to Mars to investigate a series of murders in which Rouge is the prime suspect. As the duo digs deeper into their hunt for the Immortal Nine, they uncover significant information about the rogue androids and the organization they serve.