[Bill just chuckles at Lucca's discovery of her gem, and her embarrassment. It's always amusing to see the reactions.]

'Fraid so! Sure, I can give you the low-down!

Basically, we've all been summoned to this dimension and had our energies - life forces, souls, whatever ya wanna call 'em - contained inside our gems! Why?! We have no idea!
By the way, this means your body's now a construct! The REAL you is in the gem! So don't worry about getting "fatally" injured, as long as your gem is alright you'll be fine and regenerate another body, good as new!