Betrayal

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Not only Invidia was an incredibly powerful sword if what he talked about draining the energy and powers of his wielders was true, but he's also an Ego Weapon! He spoke about the ancient Vampire Emperor using the Soul-Ego-Forging "Technique" to create an Ego by sacrificing one million demon souls… I guess he was able to create something this strong with measly mortal souls after putting up a million of them. Not only he had grown over hundreds if not thousands of years, but he also holds the power of previous Human Emperors which he had stolen their powers and devoured their souls over time.