After a fire destroyed their village and killed their parents, Mamoru and his older sister, Kotone, were adopted into the wealthy Kamishiro household. Years later, Mamoru now serves as the household's butler. As a matter of fact, however, the Kamishiro family harbors a dark secret: its wealth and influence stem from a ritualistic orgy known as the "Feast." Kamishiro women are renowned for their passion, fertility, and unrivaled offspring quality. During the Feast, influential men from around the world pay handsomely to fertilize these peerless wombs. Meanwhile, the bedridden Kamishiro head Ikki faces exile by the end of the month if he cannot impregnate his lovely wife, Saya, with the next heir. Ikki calls for a new feast with Kotone as the offering in response to pressure from his clients and the scheming lieutenant Shinohara. With clients swarming to the manor like locusts, Mamoru is thrown into a nightmare. Can he protect Kotone, Saya, and his younger stepsister Ririko from the Feast until the end of the month?