You gain the Aegis from the Xenoblade universe, its power is localized reality manipulation via higher dimensional energy from a conduit. Or in layman's terms anything you imagine becomes real, within reason, depending on your total power output. Your blade is powered by a connection to a conduit that cannot be reached or tampered with, don’t want another incident on our hands. Your blade is also a person, this person can be Pyra, Mythra or both at the same time, your choice. Although that doesn’t matter too much outside of their appearance since they are fundamentally the same person. The more you work with and resonate with your blade the greater the power you can wield.