In the Kingdom of Girtonia, Philia Adenauer is the latest in a long line of saints, renowned as the greatest and most powerful in history. Her prodigious talents in magic, medicine, and barrier creation have protected the kingdom from monsters and calamities for years. She is also the fiancée of the second prince, Julius. Despite her invaluable service, Philia is widely disliked by the nobility and common people alike, who find her expressionless demeanor, relentless perfection, and lack of overt charm to be cold and unapproachable.

Exploiting this sentiment, Prince Julius publicly breaks off their engagement, accusing Philia of being too perfect to be likable. In a cruel act of political and personal convenience, he then sells her to the neighboring Kingdom of Parnacorta in exchange for gold and resources, as Parnacorta recently lost its own saint and is in desperate need of a replacement. Philia's own parents, Georg and Cornelia, complicit in the transaction, prioritize the monetary gain over their daughter's welfare. Expecting further mistreatment as a discarded tool in a foreign land, Philia steels herself for a lonely existence. However, upon her arrival in Parnacorta, she is met with a warm welcome, kindness, and genuine gratitude from its citizens and the royal family, including Prince Osvalt, who encourages her to rest and discover a life beyond constant labor.

As Philia begins to flourish in her new home, using her abilities to erect barriers and cure epidemics, Girtonia begins to crumble. The kingdom quickly realizes that Philia had been secretly performing the work of entire governmental and magical departments, and without her, monster incursions rise and infrastructure fails. Back in Girtonia, Philia's younger sister, Mia, who genuinely adores her sibling, refuses to accept the official story of Philia being "sent away." Horrified by her parents' and Prince Julius's cruelty, Mia fakes acceptance of Julius's marriage proposal as part of a scheme to gather evidence and enact revenge on those who wronged her sister. While Julius, an incompetent and narcissistic manchild, proves unable to lead, Mia works to expose the conspiracy behind Philia's sale.

Major narrative arcs include Philia adapting to a healthy lifestyle and the slow realization that her emotionless facade was a defense mechanism developed from a lifetime of emotional abuse and exploitation. Later volumes expand the scope, revealing a deeper conspiracy when Philia is named the successor to the papacy, forcing her and Prince Osvalt to investigate the tampering of the late pope's will. A significant revelation also emerges: Philia is not the biological daughter of Georg and Cornelia but was stolen as an infant from her true mother, Hildegard, the previous saint, adding a layer of generational tragedy to her abandonment. While Philia finds happiness and purpose in Parnacorta, the narrative maintains a dual focus on Mia's dangerous quest for justice in the decaying Girtonia, leading toward an inevitable confrontation between the sisters and the kingdom that threw Philia away.