Celia Mauser is a pivotal figure whose origins lie far in the past of the world's history. Existing in an artificial body, she has maintained her appearance for approximately five thousand years. She is revealed to be the original Lord Mauser, and the protagonist Pacifica Casull is a physical recreation of her. This explains their striking resemblance, though Celia possesses lighter hair and a more mature appearance compared to the young Pacifica. Her familial connections are also mirrored in the present, as she had siblings who greatly resembled Pacifica's adoptive brother and sister, Shannon and Raquel.

In the distant era of the Genesis Wars, which took place five thousand years before the main story, Celia served as a seer. Her ability allowed her to read enemy movements with great accuracy, making her a valuable asset in humanity's conflict against alien forces. Despite her crucial role, she ultimately made a choice that would seal the fate of humanity for millennia. She betrayed her own people in an attempt to save her brother, a D-knight like Shannon, and her sister. This act of familial loyalty led directly to the Peacemakers, also known as the Valkyrie Type, being brainwashed. As a consequence of this betrayal, humanity was sealed within a controlled world called Providence. It is a deep irony that the Peacemakers, who follow her commands, are unaware that she is a human woman, and most of them harbor an intense hatred for humanity as a result of their brainwashing.

Celia's motivations stem from this ancient history and the decision she was forced to make. Her role in the story is primarily as the final arbiter of humanity's fate. After Pacifica is killed by her twin brother Forsyth, her consciousness meets Celia in a virtual space. Here, Celia explains that Providence was a created, ideal world meant to protect humanity from a greater threat, but also to control them. She presents Pacifica with the ultimate choice: to preserve the sealed, peaceful world of Providence or to destroy it, freeing humanity to make its own decisions, for better or worse. This moment is the culmination of Celia’s long vigil, as she has waited for the Providence Breaker, Pacifica, to be strong enough to make this decision. Her character undergoes its final development when Pacifica chooses freedom. Accepting this decision, Celia smiles and expresses her own relief, stating that she is finally free to join her deceased siblings, before she disappears along with the Providence she helped create. Her notable abilities include her former power as a seer, which was instrumental in the ancient war, and her absolute authority over the Peacemakers.