The Moonlight Stone (月の石 Tsuki no Ishi, lit. "Moon Stone") is an object which was made by the evil mamodo, Zofis. It was used to manipulate the hearts of the many humans and Ancient Mamodo who fought in his "army". That object produces a light which can replicate that of the moon, and initially was used to free all the ancient mamodo from their Stone Tablets. The Moonlight stone also has the ability to heal wounds and restore the heart energy of humans, who have their minds and heart controlled so that they do anything that their mamodo partner wants, like cast a spell, without the mamodo saying anything. However, not all the humans who fought with the ancient mamodo had their minds controlled, like Gensou, Dalia Anjé and Robert Vile.
The Moonlight Stone was protected by Demolt, a massive mamodo who wasn't very smart. Because of the stone, a squad of six mamodo teams: Zatch Bell and Kiyo Takamine, Tia and Megumi Oumi, Kanchomé and Parco Folgore, Ponygon and Kafka Sunbeam, Wonrei and Li-en and Kido and Dr. Riddles, make an invasion to the Devolo Ruins and attempt to destroy the Moonlight Stone. Eventually, it was destroyed by none of those mamodo teams, but by Penny and Uri, with help from Byonko and Alvin, using her strongest spell So Giaku.