In the medieval fantasy world of Álfheimr, succubus princess Astarotte Ygvar, the first princess of the kingdom of Ygvarland (ユグヴァルランド, Yuguvarurando?), has just reached the age of 10. 10 years old is a special age for a young succubus, as it is when they are traditionally expected to form a male harem.

In order to maintain their body and preserve their beautiful appearance, Succubi who have undergone puberty must consume male essence, much like how a vampire must consume blood. Initially a mere kiss will suffice, however as Succubi mature into young adults they eventually need to consume a liquid called "sáðfryma," better known as semen, to sustain themselves. The harems they form ensure a steady and safe supply of the liquid.

The princess, however, bears a great dislike against men, and only agrees to create a harem if a human male is to join, as humans are said to be extinct. However her followers are somehow able to find a human male named Naoya Tohara who, along with his daughter Asuha, is brought to the demon world to be part of Astarotte's harem.

Lotte no Omocha! (ロッテのおもちゃ!, Rotte no Omocha!, "Lotte's Toy!") is a Japanese manga series written and illustrated by Yui Haga about Naoya, a man brought to a magical world as a candidate for the Princess Astarotte's harem. Lotte no Omocha! began its serialization run in the July 2007 issue of Dengeki Maoh and later republished in collected volumes by ASCII Media Works. In 2011, the manga series was adapted into an anime television series under the title of Astarotte no Omocha! (アスタロッテのおもちゃ!?, "Astarotte's Toy!"), produced by Diomedea under the direction of Fumitoshi Oizaki which aired between April and June 2011.