The story begins with Sophia Moriath, the Saint of the Border Tower, being informed by Neymar, a court magician, that her twenty-two-year tenure protecting the human world from demonic creatures is coming to an end. At forty years old, Sophia is considered past her prime for the role, which requires high magical power and singing ability to perform "curse songs" from the tower's rooftop stage. These songs pacify demonic entities, who are drawn to beautiful human music. A strict rule for Saints is the prohibition of romance, as scandals are believed to provoke demonic attacks. Sophia, who became Saint at eighteen due to her predecessor's scandalous marriage, found the isolated life at the tower, with its simple duties and provided meals, surprisingly comfortable, especially compared to the social life she disliked.
Upon her retirement, Sophia is to return to the capital. However, she is uncertain about her future, as historical precedent suggests Saints often marry into noble families, and at forty, she feels her prospects are limited. She recalls a past offer of marriage that was interrupted by a demonic surge. Her royal lineage, though direct, is considered low-ranking due to her mother being an orphan raised in a temple, making her a less desirable political marriage candidate for her half-brother, the Emperor. Sophia suggests staying at the tower to compose music or assist the new Saint, but Neymar firmly rejects this, emphasizing the Emperor's anticipation of her return.
General Grau arrives with an escort to accompany Sophia back to the capital and to protect the new Saint, Riina, a sixteen-year-old relative of Sophia's. Grau, a handsome and capable man Sophia knew since her arrival at the tower, had previously promised to escort her upon her retirement. He is a recurring figure at the Border Tower, and his repeated assignments there, despite his elite status, remain a mystery. Sophia considers him a rare friend.
The handover ceremony involves Sophia and Riina performing a duet. The demonic creatures react to their curse songs with a display of lights and a rumbling sound interpreted as a standing ovation, signifying their approval and appreciation. Riina, deeply moved by this unprecedented connection, sheds tears. Sophia, exhausted from singing five songs, collapses after an encore, a testament to her dedication.
The next day, Sophia departs for the capital. Grau, now a General, escorts her. He expresses admiration for the ceremony and Sophia's performance. During their journey, Sophia experiences a moment of weakness, attributing it to magic depletion and age, reinforcing her decision to retire. Grau carries her to the carriage, his strength and gentle demeanor causing Sophia to blush. He confesses he has a person he wishes to marry but cannot reach, implying a long-held, unrequited affection.
Upon arrival at the palace, Sophia is met by Neymar and then by her half-brother, the Emperor. He expresses relief at her return and gratitude for her service, apologizing for not recalling her sooner due to his mother's influence. The Emperor reveals a plan for Sophia: a recital for the soldiers who missed the handover ceremony, as many have become her fans during their service at the Border Tower. He also mentions an impending "consolation party" and hints at a reason for her early retirement that is being kept secret. Sophia is bewildered by the idea of a recital and the notion of having fans among the soldiers, as the curse songs are meant for demonic beings.
Neymar arranges for a new Saint's robe for Sophia, explaining it's for her protection and to maintain her image as a Saint for the upcoming events. Sophia is taken to a military barracks for a rehearsal, accompanied by Grau, who insists on escorting her despite her protests. During their visit, they encounter Bulga, a Staff Chief, who expresses his eagerness to attend the recital. He reveals that the demand to attend is so high that a lottery might be necessary. Sophia is surprised by the overwhelming interest.
Later, while rehearsing a simple curse song, Sophia's voice carries beyond the hall, attracting the attention of many soldiers outside. She realizes the curse songs have a wider reach than she anticipated. Grau praises her solo performance, and Sophia feels a surge of pride and happiness. She playfully asks Grau if he would accompany her to the demon forest to thank the creatures, a request he accepts, albeit with a solemn expression. They then encounter Bianca, Grau's adopted daughter, who brought muffins for the soldiers. Sophia feels a pang of loneliness seeing their happy family dynamic.
Sophia learns from Neymar that her return to the capital is part of a larger political scheme. Many individuals, particularly from the military, are seeking to influence her through marriage proposals and business dealings, aiming to leverage her connection to the Emperor. To prevent this and to identify potential adversaries, her return and future plans are being kept secret. Sophia realizes her value is now political, not personal, and that her marriage will likely be a strategic alliance.
During a rehearsal, Sophia is drugged with a herbal tea offered by Amy, a former Saint candidate and now a Duchess. She awakens bound in a room, facing Amy, her husband Duke Desond, and their son, Louis. They reveal their plan to force Sophia into marriage with Louis to gain political power and depose the Emperor. Sophia vehemently rejects their proposal, pointing out the age difference and the lack of benefit for Louis. She argues that her influence over the military is exaggerated and that they have miscalculated.
Suddenly, a swarm of bats, revealed to be demonic creatures, invades the manor, causing chaos. Grau and his soldiers arrive, engaging the Duke's private guards. Grau quickly incapacitates Louis. As Amy holds Sophia hostage, Grau defeats Amy and apprehends the Duke and his family. Grau explains that the bats were drawn by Sophia's curse song and that he followed their trail. He reassures Sophia that he will always protect her, and she realizes his affections are not romantic but a deep loyalty.
On the day of the recital, an unprecedented crowd gathers, including soldiers, the Emperor, Neymar, and Grau. Sophia performs with immense emotion, feeling the culmination of her twenty-two years of service and the happiness of being appreciated. She concludes with a heartfelt thank you, feeling she has given her all. The recital is a resounding success, filled with cheers and applause, a stark contrast to her solitary life as a Saint.
