The Philosopher's Stone.
It was a relic of the ancient civilizations, lost in time. Only it wasn't lost, but hidden. The last demon king had found it, and that's how they could wage countless wars with no setbacks.
Not only did the stone grant immortality to the Demon King's loyal subjects, but it also gave them gold to keep fighting while draining the world's resources at the same time.
It wasn't until the Virtues defeated the demon king that they found it in his treasury.
That was the tale everyone was fed. But Aaran never believed it. The story had too many plot holes. If the stone could grant immortality, then how were the demon king and his commanders killed?
No one ever talked about that.
Now Aaran knew why.
To fight off the effects of the Philosopher's Stone, the Necromancer's Stone was created.