A count's daughter named Airi is forced by her younger sister to become a substitute fiancée, heading to the royal palace in her sister's place to enter an engagement with the king. The king, Gilheart, is rumored to be a beast due to his silver wolf blood, and Airi believes her life is over if her true identity is discovered. On her first night, she is summoned to his chambers, but the supposedly ferocious king suddenly becomes docile and asks her to pet him. This sudden change is linked to the legend of the "Moon Saint," a woman with the power to calm werewolves, a power that Airi unconsciously possesses.

Airi is a kind and humble young woman who has been treated poorly by her family, while Gilheart is the werewolf king who, despite his intimidating reputation, becomes affectionate and dependent on Airi like a loyal dog. The story takes place in a fantasy kingdom where the royal family carries the blood of the silver wolf. To formalize their union, the pair must successfully complete seven marriage rituals.

After passing the first ritual and deepening their trust, Airi's identity as a substitute is exposed by political factions opposing the Moon Saint. She tries to step down, believing her role is over, but Gilheart refuses to let her go and only intensifies his efforts to complete the marriage rituals. The arrival of a woman claiming to be the true Moon Saint and the appearance of Gilheart's younger half-brother, Julian, create further misunderstandings that drive the couple apart. Julian, who is antagonistic toward Gilheart, kidnaps Airi and proposes marriage to her himself. The pair later travel to the Sage's Forest to investigate poachers, where the proximity to the sacred land causes Gilheart's wolf instincts to grow stronger. In the forest, a sage wolf named Shiro takes an interest in Airi, forcibly courting her and later trying to lure her to the demon realm, revealing that her power as the Moon Saint is extraordinarily rare. After overcoming these trials and the trauma from their respective upbringings, the couple finally solidifies their bond and moves toward a happy ending.