That's not how it works.

[ Not like Mithos would know anything about that, right? It's not like he's a member of Cruxis. But Mithos sees no reason not to answer Lloyd's question ]

I don't know about Presea, but Colette chose to. If you take the Cruxis Crystal off of them, they'll die. Or worse, become an Exebula.

[ As for Presea, as far as he can tell, her Cruxis Crystal is artificial. Either that, or she never did anything to fully awaken it, or she'd be an angel by now. ]