Based on the game by Atelier Kaguya.

Former reporter Tokitsu Daisuke arrives at a suspicious western-style mansion built on a hill overlooking a provincial village. Awaiting him there is the mansion’s mistress, Kiriya Sumi, and her beautiful daughters.

Sumi informs Daisuke that he has been chosen to become the next patriarch, the sole male member of the Kiriya family. In return, all he has to do is impregnate one of her daughters.

However, the Kiriya carries a dark secret within their bloodline which may well have severe repercussions for Daisuke…

~ translated and adapted from official site by Cranston