Succubi are a race of beings who survive by having a harem of men from which they can suck 'life essence' from. However, Astarotte Ygvar, the crown princess, hates men. Under relentless pressure from Judit, her chief of staff, to grow up and start building her harem, she agrees to start but only with a human male. In the Creature World, humans are considered mythical creatures, with none having been seen in a thousand years. To her dismay, Judit manages to travel to the human realm and return with a 23 year old human male named Naoya Tōhara, who accepts the offer to found Astarotte's harem.

Naoya feels conflicted by the appearance of Mercelida, who three years after their chance fling left Asuha with him and disappeared, with Mercelida immediately running off before listening to what Naoya has to say. Judit reveals to Naoya that Mercelida is the queen, making Asuha and Astarotte half-sisters, and asks him to keep it a secret from Astarotte. Wanting to speak with Mercelida, Naoya and Asuha sneak into the palace dressed as maids. They are discovered by one of the queen's servants but is coincidentally chosen to be an escort based on Mercelida's requests. Upon meeting her, Naoya gives his thanks to Mercelida for bringing Asuha into his life. As Naoya talks with Mercelida, it is revealed she hid Asuha in the human realm to avoid the same battle against sisters for the throne that she faced. Noticing Astarotte is still downhearted, Naoya asks Mercelida to visit her class for the day, making it a day where everyone's parents could visit. Afterwards, Astarotte and Mercelida manage to reconcile with each other.