Cocytus Arc

This necklace is the vessel for the soul of the Demon Guilias, who was famed for his valor and cunning. Whoever wears it can acquire power beyond human understanding, but in exchange they must give up their own life. Because of this terrible requirement, for a long time it remained hidden deep within ruins once ruled by the Gods, but a thief driven by Guilias' temptation sneaked into the ruins and returned it to the outside world. Since then, the necklace has consumed countless lives and longs for new hosts even now.