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GA.png Non-Canon: REMINDER! This page is considered as among one of the many pure game contents found exclusive in Mass for the Dead only. It includes the new standalone characters that had a first-time appearance in the game. Meanwhile, the old characters had a different role and fate than from the main storyline in the official books. For that reason, it has no connections to the canon story materials of Overlord Light Novel series. The content that you had read here are based on the Overlord mobile game.

Promise Stone (約束の石) was an item used to summon the Legendary Mermaid.


According to legend, it is described to be used to summon the Legendary Mermaid when the stone resonates and is tossed in a specific pool at when four certain stars shine brightest.[1]


A beautiful translucent stone, that one can be able to see the cross sections by adjusting the light.


Promise stones appear to bear a weak magical power to them. However when a magic caster pours their power into them, they cause the stone to glow white and create a resonance. This sound while audible in air is amplified when it is placed underwater, calling the Legendary Mermaid to come.


  • A fragment of this item was passed down through the ages at a small seaside village in the Re-Estize Kingdom where the legend of the Legendary Mermaid originated.