Nanako Takashiro, the sole daughter of the noble Takashiro family—a lineage descended from historical daimyos—is afflicted by a chronically weak constitution that confines her to a bedridden existence dominated by sleep. Despite her isolated and infirm life, she nurtures secret romantic and lustful feelings for Yujiro, the family's adopted son, who struggles to manage their dire financial situation. The family's shameful economic decline, brought about by poor management from its current head, has left them vulnerable. A dark conspiracy, engineered by a rival family, targets the Takashiro assets with a specific focus on Nanako. This scheme forces Yujiro to depart, leaving the family defenseless against mounting debts. Faced with insolvency, Nanako receives an immoral proposal to work off the financial obligation through physical means, an arrangement in which her mother is complicit.