An ill-fated accident leaves a young woman named Hina orphaned and stripped of her family’s fortune. Once the daughter of a marquis, she is now scorned by society as the Ruined Mansion Lady, yet she continues to live with dignity while enduring relentless harassment from her uncle Hisanao, who harbors an unhealthy obsession with her late mother. Her lonely life takes an unexpected turn when she encounters Taka Tokimiya, a ruthlessly efficient and handsome young businessman from a count family who is known for his cold demeanor.

Taka, who is entangled in a succession dispute within his own family and driven by a desire for revenge, makes Hina a startling proposition. He proposes a strategic contract marriage, asking her bluntly to become his wife so he can utilize her noble lineage for his own ambitions. In exchange for accepting this transactional union, Hina negotiates one condition: that Taka will help her recover her mother’s treasured keepsake, which was stolen by her scheming uncle.

The story follows Hina as she enters Taka’s dangerous world, which is filled with enemies and complex political maneuvering. Despite the marriage being a mere formality, Hina faces every challenge with the refinement and intelligence she inherited from her parents. Her practical skills, particularly her talent for crafting elegant clothing, soon become a valuable asset. The quality of her work gains renown in high society, indirectly aiding Taka’s business ventures and proving that Hina is more than just a noble name. Her wise and resilient nature gradually thaws Taka’s frozen heart, causing genuine feelings to develop between them, complicating their purely contractual arrangement.

As the narrative progresses, Hina’s position is threatened by the return of Taka’s former fiancée, Nene, who uses her wealth and status to try and win him back, forcing Hina to confront the fact that their marriage was built on an agreement rather than love. The final major arc centers on the Tokimiya family’s succession struggle, where Taka must compete with his half-siblings, Haruka and Yuuki, to solve a riddle posed by the family patriarch. This contest for power ultimately forces Hina and Taka to define what their relationship truly means beyond their initial contract.