Astarotte's Toy - Season 1 Episode 6 Caret of Being Lost

As Astarotte receives tickets to an amusement park, she becomes irritated with everyone making use of Naoya. Later that night, Astarotte goes missing before Naoya finds her by the World Tree. As Astarotte yells at Naoya, she accidentally activates the gate and is sent to the human world. Trying to think of a way to get her back, Naoya and Asuha go to seek out a sage named Sorveig that could help them. In order to see her, they have to solve a riddle, which Asuha manages to answer with her undies. There, they meet the sage, Ingrid Sorveig Sorgrims, who reveals the gate is linked to the Succubus race. As Ingrid agrees to help them, she soon learns that, due to the lack of magic in the Human World, Astarotte doesn't have enough magic to activate the gate.