The Dark Stone (魔石 Maseki lit. Demon Stone) is the half of the Sacred Stone of Grado, which was previously known as the Fire Emblem, containing the Demon King Fomortiis's soul. This stone was created when Lyon resurrected his father, Emperor Vigarde, after studying the power of the "Fire Emblem". He splits the "Fire Emblem" into the Sacred Stone of Grado and the Dark Stone. He uses the Dark Stone's power to revive Vigarde, though as an empty puppet instead of truly returning him to life as Lyon had wanted. When confronted by Knoll, one of the mages who worked with him on studying the "Fire Emblem", he crushes the Sacred Stone in front of him and sentences Knoll to be executed to keep the truth behind the Dark Stone from being revealed. Afterwards, he carries the Dark Stone with him everywhere. During the invasion of Renais, Lyon uses the stone again to created a puppet of Monica after Orson betrayed both his country and prince, Ephraim. The use of the Dark Stone causes Lyon to be possessed by the Demon King, though whether Lyon overcomes it or succumbs to it depends on the route chosen by the player.
- In pre-release materials for The Sacred Stones there are images of monsters using a weapon called the "Stone Shard"; the item remains in the final release, though unused. The connection of the items is not as evident in the English name, but in the Japanese version, the item is known as "Demon Stone Fragment", implying that the monsters were using shards of the Dark Stone itself.