The story begins with the protagonist, Aria, discovering her lover, Sirius, the second prince and head of the First Magic Division, embracing her sister, Roselia, and confessing his love. Aria, who had been praying for Sirius's recovery from a royal illness called "Dragon Demon Syndrome," is devastated by this betrayal. She flees the scene, accompanied by her subordinate, Vass, who expresses concern. Aria had intended to give Sirius a birthday gift, but now her world is shattered.
Later, at a tavern, Aria drowns her sorrows with apple sparkling juice, lamenting Sirius's apparent preference for her beautiful and talented sister. Her companions, Bianca, Rex, and Dan from the First Magic Division, try to comfort her, though Dan's insensitive remark about being dumped nearly escalates into a magical confrontation. Aria reveals that Sirius has chosen her sister, whom everyone adores as a saint. Bianca offers solace, while the men try to lighten the mood with jokes and offers to listen.
Aria returns to her dorm, feeling more at home there than in her ducal residence. She encounters her sister, Roselia, who returns a stolen stole and brooch. Roselia apologizes for her involvement with Sirius, explaining that she stayed by his side while Aria was away on a dangerous mission to retrieve dragon scales for a cure. Roselia, a renowned healer, admits her magic was insufficient for Dragon Demon Syndrome, but she felt compelled to keep Sirius alive until Aria's return. Aria, though hurt, accepts her sister's explanation, acknowledging her sister's superior abilities and her own perceived shortcomings. She offers congratulations on Roselia's upcoming engagement to Sirius, a difficult sentiment to express.
Aria reflects on her family's neglect and her sister's consistent kindness. She recalls her past ambition to become the head of the First Magic Division to support her sister. A flashback reveals a conversation with Sirius during their academy days where he confessed his feelings for Aria, stating he saw her as more than a friend and that he had never seen her as just a "girl" until then. He proposed they become a couple, leaving Aria flustered and her heart racing.
Another flashback details a practical exam in a dangerous forest near Dragon Valley. Sirius, clearly upset by Aria's avoidance, confronts her. He reveals that their colleagues, Bianca, Rex, and Dan, were aware of his feelings for Aria, which Aria had been oblivious to. Sirius challenges Aria to a bet: if he wins the exam, she must stop avoiding him; if she wins, he owes her a favor. During the exam, Aria and Vass venture into a restricted area after seeing figures, leading to an encounter with dangerous monsters. Sirius arrives just in time to save Aria, who is struggling with her magic due to her emotional distress. He encourages her to regain her confidence, reminding her of her goal to become stronger for her sister. They fight together, and Aria's magic returns. However, Sirius is injured while protecting her. As they escape, Aria confesses her love for Sirius, who, despite his injury, expresses his own feelings and his desire to live for her. They are rescued, and Aria, exhausted, falls into a deep sleep.
A week later, Aria is preparing for a monster survey mission. Her colleagues, Vass, Dan, Rex, and Bianca, reveal they are also leaving the Magic Division due to their dissatisfaction with the new management structure under Aria's father, who has taken control of both the Magic and White Magic Divisions. They express their loyalty to Aria and their disdain for her father's arrogance and the perceived manipulation of Sirius's intentions. Bianca specifically voices her dislike for Roselia. Aria, though touched by their support, decides to proceed with her mission, intending to visit Dragon Valley to fulfill a promise.
Aria's father confronts her, disowning her for not supporting her sister's engagement and ordering her to leave the duchy and the Magic Division. Her colleagues defend her, but her father dismisses their protests, revealing that Sirius will be stepping down from his position and that the Magic Division will be integrated with the White Magic Division under his control. He claims Sirius has agreed to Aria's dismissal. Aria, heartbroken but resolute, accepts her father's decree and announces her departure to Dragon Valley. Her friends, though saddened, pledge their support and depart on their own paths.
Aria, accompanied by Vass, ventures into Dragon Valley to seek the dragon's help for Sirius and the Crown Prince's Dragon Demon Syndrome. They are attacked by powerful monsters. Vass is killed, and Aria, despite her efforts, is overwhelmed. Suddenly, a silver dragon appears, and Aria, remembering her mission, pleads for its help. The dragon, initially dismissive, becomes intrigued by Aria's brooch, which contains dragon magic. It agrees to provide scales for the cure and a protective charm for Aria, but warns her to return with a promised payment, even if the princes have already died. Aria vows to return and sets off for the capital with Vass's body.
The narrative concludes with Aria reflecting on her past and the events that led her to this point, emphasizing her determination to fulfill her promise and her complex feelings for Sirius.
