Pacifica Casull is the main protagonist of Scrapped Princess. She was born as the younger of twins to the royal family of the kingdom of Leinwan, making her a princess by birth. According to the 5111th Grendel Prophecy issued by the Church of Mauser, a princess born on the continent would be a poison that would destroy the world upon reaching her sixteenth birthday, and Pacifica was identified as that child. To prevent the prophecy from coming true, she was ordered to be executed as an infant and was thrown from a cliff, an act that gave her the name Scrapped Princess. She survived the fall and, through the efforts of those loyal to her birth mother, was taken in by the Casull family, commoners who raised her as their youngest daughter. Her adoptive parents named her Pacifica, after an ancient word for peace, in the hope that she would not bring about the end of the world.

At the beginning of the story Pacifica is a fifteen-year-old girl with blonde hair and blue eyes who resembles her biological mother. She grew up in a warm and comfortable household, which shaped her into a generally cheerful, sweet-natured, and somewhat spoiled young woman. She is youthful, innocent, and tends to be naive and trusting, sometimes placing confidence in people even when caution would be wiser. Because she was protected for most of her life, adjusting to life as a hunted fugitive is difficult. She has no combat training and cannot defend herself, and her dependence on others becomes a recurring source of self-doubt. She also struggles with the prophecy itself, wondering how so much suffering can be caused by her mere existence and blaming herself for the misfortune that follows her.

Her central motivation is to survive and to understand the truth about herself. Despite the danger, she maintains a bright and optimistic outlook on life and wants to live normally, free of the label placed on her. When her survival is discovered, assassins are sent after her and her adoptive father is killed, forcing her to flee the kingdom. From that point she travels across the continent with her adoptive brother Shannon, a highly skilled swordsman, and her adoptive sister Raquel, a powerful magician, who both swear to protect her even at the cost of the world. Along the way she meets a variety of allies and enemies, including the mysterious girl Zefiris, an ancient weapon known as a Dragoon who aids the party, and a young knight named Leo who constantly professes his love and desire to marry her, a courtship she deflects in a lighthearted manner.

Her role in the story is that of the world's central contested figure. The Church of Mauser and the general populace pursue her out of fear, while the true powers behind the prophecy, four godlike beings called Peacemakers, secretly manipulate events to have her eliminated. The Peacemakers are unable to act against her directly and instead work through human agents. Over the course of the series it is revealed that the fantasy world is actually Earth in the distant future, sealed off by the Peacemakers after a war with alien foes. Humanity was imprisoned in an artificial medieval society and kept under mental control through a system called Providence, which renders humans unable to resist the will of the Peacemakers. Pacifica is the only human in five thousand years who is immune to this control, and on her sixteenth birthday that immunity will spread to others around her. Far from being the destroyer of the world, she is actually its liberator, the result of a plan devised five thousand years earlier to free humanity. She is therefore known to some as the Providence Breaker.

Her abilities are not those of a warrior or a mage. Instead, her power lies in her immunity to Providence and to the influence of the Peacemakers. When she is under extreme emotional distress, she can release bursts of her inner power that sever the connection between those nearby and Providence, restoring their free will. This ability is what makes her so dangerous to the Peacemakers and so important to the future of humanity.

Her key relationships are with her adoptive siblings. Shannon acts as her guard and protector, a brother devoted to her safety, while Raquel serves as both caregiver and powerful magical support. Zefiris becomes a companion and defender who fights alongside the family, and her bond with Pacifica deepens as the truth is uncovered. She also has a complicated relationship with her biological twin brother, Prince Forsyth. Having witnessed the suffering caused by the Peacemakers' attempts to eliminate his sister, he requests a meeting with her and uses the opportunity to stab her in the back, ten hours before her sixteenth birthday. This act sends her into the phase sphere, where she meets Celia Mauser, the powerful psychic whose mind was used as the basis of the world's control system. Celia offers Pacifica the choice of whether humanity will remain in its protected cage or be set free. Though Pacifica is sympathetic to the idea of a safe, sheltered world, she ultimately chooses freedom, allowing humanity to make its own choices. This decision destroys Providence, frees mankind, and Pacifica is resurrected and returns home to live on the family farm with Shannon, Raquel, and Zefiris.

Through this experience she grows from a sheltered, self-doubting girl into someone who accepts the weight of her origins and makes a deliberate choice for the future of all people. Her development is defined by that choice, as she moves from being defined by a prophecy about destruction to being defined by her own decision to grant humanity its freedom.