I have a suggestion regarding the relic's power source and how it actually chooses its wearer.

Everyone has a little bit of magical energy inside of them, but those levels frequently aren't enough to rationally sustain relics; users of the artifacts usually have a stronger, more abundant supply than most people, above average let's say. As for how it chooses its wearer, there must be (a) certain condition(s) to be met. For example, Kaiden's bell relic requires the user to be blind. That makes sense, right? But then we have Shin, and let's say that the Mask's conditions were that someone who wears it must be used to following orders without question, but has a potential for making individual thoughts and ambitions outside the instructions (I know this wording is a bit weird, sorry)!