"Scrapped Princess Supplement" is a manga series that expands on the narrative of the original "Scrapped Princess" light novels and anime. The story is set in a fantasy world where magic and technology coexist, blending elements of science fiction and medieval fantasy. The central figure is Pacifica Casull, a young girl prophesied to bring about the destruction of the world on her 16th birthday. Labeled as the "Scrapped Princess," she is marked for death by the ruling religious order, the Peacemakers, who believe her existence threatens the stability of their world.

Pacifica is protected by her adoptive siblings, Shannon and Raquel Casull. Shannon, a skilled swordsman, and Raquel, a powerful sorceress, are fiercely loyal to Pacifica and dedicate themselves to keeping her safe from the relentless pursuit of the Peacemakers and other factions seeking her demise. The trio embarks on a journey to uncover the truth behind the prophecy and Pacifica's role in it, encountering allies and enemies along the way.

The narrative delves into themes of fate, free will, and the consequences of human ambition. As Pacifica and her siblings travel, they uncover secrets about the world's history, including the origins of the Peacemakers and the true nature of the prophecy. The story reveals that the world is a post-apocalyptic society where advanced technology from a previous civilization has been misinterpreted as magic. The Peacemakers, who control this technology, manipulate the population to maintain their power, using the prophecy as a tool to suppress dissent.

Key characters include Zefiris, a sentient weapon from the ancient civilization who becomes an ally to Pacifica, and Christopher Armalite, a high-ranking Peacemaker who grapples with his loyalty to the order and his growing doubts about their methods. The series explores the moral complexities of its characters, presenting them as multifaceted individuals with conflicting motivations.

The plot builds toward a climactic confrontation as Pacifica's 16th birthday approaches, forcing her to confront her destiny and the choices that will determine the fate of the world. The resolution ties together the threads of the narrative, addressing the prophecy's origins and the true purpose of Pacifica's existence. The series balances action, intrigue, and emotional depth, offering a compelling exploration of its central themes within a richly constructed world.