Mistaria Rilfarde, the daughter of a failing viscount house, has just been publicly disowned by her fiancé, Harold Ilnston. His reason is a simple one: she lacks charm as a woman. For Harold, who has his eyes on the more traditionally feminine Dorotea, the engagement is merely an inconvenience to be discarded. For Mistaria, known as Mithril, the broken engagement is not a source of heartbreak but a practical crisis. With her parents dead and the financial support from her fiancé’s family about to vanish, the eighteen-year-old, who carries the memories of a past life in another world, decides she has only one option: she must find a job.

Her search leads her to the royal palace of the Kingdom of Eustaria and the Magicians Guild. Specifically, she applies to a section known as Violet Water, a division specializing in curses, status ailments, and dangerous magical research. The place is a notorious disaster zone, a veritable demon's den so filthy and chaotic that the other two divisions, Ruby and Amber, have demanded it be cleaned up. The job posting seeks resilient, discreet, and hardworking individuals, and Mithril, with her pragmatic, working-class sensibilities from her previous life, proves to be a perfect fit. She is hired as a cleaning maid, much to the confusion of the aristocratic mages who cannot fathom a viscount's daughter scrubbing floors.

Within the chaotic halls of Violet Water, Mithril’s unwavering earnestness and resilience stand in stark contrast to the eccentric and often helpless mages. She efficiently tackles the grime, disposes of mysterious failed experiments, and remains utterly unflappable in the face of the division's strange denizens, from giant caterpillars to pet snakes. Her most notable admirer, however, is Alフリード, a powerful mage known as the Ice Prince for his expressionless demeanor and refusal to smile. Initially drawn to her dedication, his interest quickly deepens into something more personal. As they work alongside each other, Alフリード begins to shed his cold exterior, revealing a man who is kind, protective, and deeply taken by Mithril's strength of spirit.

Their relationship progresses from colleagues to lovers as Alフリード launches a sincere and persistent courtship. However, a dark shadow hangs over their growing happiness: Alフリード carries the secret of the Dragon’s Curse, a heavy burden passed down through the royal family. Fearful of how she might react to this dangerous legacy, he hesitates to reveal the truth, a hesitation that is exploited by the reappearance of his own former fiancée. Ultimately, their mutual affection overcomes these obstacles, leading to a confession, a public engagement, and a wedding.

The story follows their life together across several arcs. After getting married, they settle into a happy newlywed life, but are soon summoned by the king with unbelievable news: a dragon has been discovered in Mithril’s home territory, the Viscounty of Rilfarde. Their visit to her hometown to report their marriage is complicated by a childhood friend who vehemently opposes the union, leading to a duel over Mithril. Later, the couple faces the challenge of a new, clumsy maid assigned to Violet Water who becomes overly attached to Mithril, sparking jealousy and requiring careful handling as her mentor. Mithril’s ambition grows as she trains to become a reserve knight so she can accompany Alフリード on monster subjugation expeditions, a decision that involves a young former dragon named Laddie joining their team. Finally, when Alフリード is assigned to guard a diplomatic delegation from a neighboring country, he mysteriously disappears after the mission concludes, leaving Mithril to desperately search for her missing husband. Through all these trials, the bond between the mentally strong, mythril-hearted lady and her once-smileless magician only deepens.