is it odd that the crystal is the most interesting thing to me?
This chara, Lirea was born with a strange infection, if she's trying to use magic, she has a sort of seizure, her nose-mouth-ear and eyes are start to bleed, then the magic will fail and she'll faint. She's "allergic" to her inner magic and not abble to synchronise with it. Her only medicine is this crystal! 
ah ok. does that have to do with why her eyes are that colour as well?
Yes ^^
I never did understand the black eyes on some character so...
Lirea's white of the eye is dark because her illnes, it's a symptom.
ah