Reeva Demesne was a Mirialan scientist of the female persuasion. She initially served the Galactic Republic before transitioning to the Galactic Empire, focusing her expertise on energy-related investigations. Orson Krennic enlisted her, and she unwittingly contributed to the research and development of the Death Star's powerful superlaser weapon. For a period, she collaborated with both Galen and Lyra Erso, even attempting to warn them about the true intentions behind their experiments.
At the Futures Program institute located on Coruscant, Reeva Demesne enrolled and dedicated her studies to the various aspects of energy: its generation, enrichment, and enhancement. It was here that she encountered Galen Erso, who was then employed as a "Professor." She later provided mentorship to his future wife, Lyra Erso, who also met Galen and received a marriage proposal during this period. Demesne, alongside her friend Nari Sable, was present at their wedding ceremony. Later, her research focus shifted when Orson Krennic, recently appointed to lead the Special Weapons Group by the Corps of Engineers, drafted her into the shield generator program. This occurred at some point during the Clone Wars, where she began her work on defensive shield generators intended for use on capital ships and the Death Star battle station that was soon to be named.
In the year 21 BBY, after Galen had been rescued from unjust imprisonment on Vallt, Demesne and Galen were reunited on Coruscant for the first time in several years. Before their conversation ended, she extended an invitation to him for an upcoming alumni reunion scheduled to take place in two weeks. During the reunion, Demesne had the opportunity to reconnect and converse with Lyra after a long separation. Towards the end of the gathering, she also intervened in an attempt to diffuse a conflict between Galen and another scientist, Dagio Belcoze. Belcoze had accused Galen of being a Separatist sympathizer who had divulged Republic secrets while detained on Vallt. Belcoze later contacted Galen to apologize, attributing his outburst to the alcohol he had consumed at the event.
Sometime later, unable to reach Galen, Reeva contacted Lyra, who was taken by surprise by the unexpected communication. She inquired whether her husband had recently been in contact with Belcoze. She revealed that Belcoze was stationed on Malpaz, but quickly changed the subject. She informed Lyra that she was currently stationed on the planet of Hypori, vaguely suggesting a connection between the two planets. She also mentioned her involvement in Project Celestial Power before the call was abruptly terminated. Reeva's discomfort and ambiguous tone made it evident to Lyra that their communication was being monitored and that Reeva was unable to speak freely or fully explain the truth behind her statements. Lyra shared this information with her husband. Three weeks later, during a conversation with Krennic, Galen expressed his concerns about Reeva's assignment to Hypori instead of Coruscant, where they were supposedly working on the same research topic. Krennic, who was secretly eavesdropping on the Erso family's suspicious conversations within their apartment, anticipated Galen's concerns and promptly assured him that he would investigate the matter—a false promise that was never fulfilled.
As they delved further into the conspiracy that Reeva had brought to their attention, the Ersos came to the realization that Galen's work was being weaponized. This realization occurred after they examined sensory data from the remnants of the Hypori research station. This discovery followed the explosion of one of the Empire's so-called "energy research facilities," which occurred when an experiment aimed at replicating Galen's work secretly commenced and unexpectedly failed.
Reeva was among the key scientists who witnessed an early test firing of the superlasers being developed for the Death Star, directed at the Hero Twins black hole systems. After the successful destruction of this celestial phenomenon, she questioned Krennic about how the energy required for such a weapon would be stored. He responded by asserting that it was not her concern. When she pressed for more details about the project and expressed her desire to withdraw, foreseeing that her work would bring peace through fear, Krennic promised to "permanently" reassign her and her colleagues to another location. Shortly thereafter, he ordered the complete destruction of the energy research facility on Hypori, which was in the process of being repaired and where she was currently stationed. This action resulted in the deaths of Reeva and the other scientists present, effectively concealing the Empire's work.
Demesne possessed green skin with a powdery texture, and her face was adorned with vertical bands of dark diamond-shaped tattoos. Her lips were full and displayed an iridescent blue scale pigmentation. She had gray hair. During her meeting with Galen Erso, she was dressed in a floor-length scarlet robe and a cowl that concealed most of her hair. Lyra Erso described her as having a dark complexion and exotic facial tattoos.
Reeva Demesne made her debut in Catalyst: A Rogue One Novel, a book penned by James Luceno and published in 2016. Her character was created to advance the narrative of this prequel to the film Rogue One: A Star Wars Story, which was released in theaters one calendar month after the novel's publication.