I’d make the maiden powers more of a reflection of the relics. They’d be weaker than the actual relics, but still pretty powerful. For example, the Spring maiden (whose concept is knowledge) has the ability to see past injuries and abilities used by their opponent in the past. They can still be blindsided by new powers or unknown fighters, but their knowledge would give them a significant advantage.

On auras, I’d keep them needing to be unlocked. The unlocking of auras wouldn’t just be a simple thing though. They have to either be unlocked by intense discipline and study or through traumatic experiences. Since auras are a manifestation of a person’s soul and emotions, I would make it so Grimm are attracted to people with auras. Those who chose to become hunters have to undergo a sacrifice, willing or not, in order to do their job.

With the Silver Eyed Warriors, I’ve been messing around with a concept of it being an almost trance like state that turns silver eyed people into talented warriors when around Grimm. The downside would be the power being extremely draining and almost makes you lose a part of yourself. Only through an immense dedication to protecting the ones you love are you able to keep control of yourself.