Astarotte no Omocha! unfolds in a magical realm where succubi, including the young princess Astarotte “Lotte” Ygvar, need the life seed of men to survive, restore their magic, and continue the royal line. That rule also means every succubus is expected to keep a harem close at hand, even though Lotte herself despises men and will be in danger once she reaches maturity. To protect her future, her attendant Judith Snorrevik travels to the human world in search of a man Lotte can tolerate.
Judith returns with Naoya Touhara, a 23-year-old single father who leaves his daughter Asuha behind in the human realm. Naoya becomes the first member of Lotte's harem, but instead of treating the princess as an object of desire, he settles into life at court and tries to make her happy as she struggles with her role. The arrangement becomes more complicated when Asuha is allowed to come to the magical realm, straining Naoya's relationship with Lotte and forcing him to mend the growing rift between them.
As Naoya grows closer to Lotte, it becomes clear that his arrival in the magical realm is no accident, and that the ties linking him, Lotte, and the people around them reach deeper than either of them first realized.