Nero, is an incubus and a member of a high noble family the underworld who has four wives. His many wives all come from a different race, there's a succubus, an angel, a demon, a werewolf and an oni. They have all engaged with Nero because of the great honor and wealth it would bring them to marry with a high noble.
However, Nero is good for nothing when it comes to their relationship and isn't assertive when it comes to night activies, because of which his relationship with his wives is quite cold.
At such time, Nero's father has decided that "The first to bear a child will be granted the seat of the first wife". Since usually the standing between wives is decided by the standing of the house they originally come from, his new wives have started to assertively seek him to impregnate them.
And so, Nero's peaceful days have ended and every day he is assaulted by his wives. His erotic married life under one roof with his four wives begins!