Deep within a secluded village lies the Kamishiro household, a prestigious family whose women possess unmatched beauty. After being brought into the household following the death of his parents, Mamoru vows to repay the kindness of his benefactors by serving as their loyal butler. His older sister, Kotone, is raised as an heiress of the family. Showered with love by their adoptive mother Saya and stepsister Ririko, the two could not be happier with their new lives.
Yet despite its elegant reputation, the Kamishiro household hides a dark secret: to sustain its vast fortune and influence, women of the family are required to participate in a ceremonial orgy known as the "Feast." In this erotic ritual, men from all over the village pay a bountiful sum for a chance to bed these women. When the Kamishiro head, Ikki, is threatened with exile for being unable to bear an offspring with Saya, he declares the beginning of the next Feast to appease the villagers—with Kotone as the main offering.
As the night of the ritual draws near, Mamoru must do whatever it takes to protect the chastity of his beloved sister. Although she is prepared to carry out her duty as a maiden of the household, the defiant boy will ensure that none can bring harm to whom he loves most.