Gelda Nebilim used to be a member of the Oracle Knights of the Order of Lorelei as Locrian Colonel. Her task was to investigate Planetary Arte Catalysts, six weapons that possessed the power of Rem and Shadow, the Fonons of Light and Darkness. After retiring from the Oracle Knights, she established a school in Keterburg's Silver Town. Unlike other teachers, Professor Nebilim formed close bonds with her students and treated them as if they were her own children. She was always willing to help when needed.
When Jade Curtiss joined the school as a young boy, Professor Nebilim sensed that he had a twisted mind and could not distinguish between guilt and pleasure in taking lives. Despite this, she managed to change his perspective and encouraged him to use his Fomicry methods for a more noble cause. Additionally, she taught Saphir, who later became obsessed with reviving her.
Professor Nebilim also concealed Peony the Ninth's presence in the school from his isolated mansion, allowing him to learn and interact with other children. She believed that it was crucial for an emperor to understand their people, especially since Peony would eventually become the next ruler of the Malkuth Empire.