[And stack, they do. Leaning their cheek into his hair, plenty content with it.]

In exchange for my own gem, I gave up my sense of taste. With it, my mouth and stomach. Hence being within my abdomen.
It seemed much more convenient. Removing one's gem is not particularly difficult if it isn't hidden away.

[They've seen what happens if a gemstone gets removed somehow - the others have gone temporarily blind without theirs, after all. That doesn't sound, y'know, fun.
Plus, it's just another way of concealing any weaknesses. They don't need those. Weaknesses are for, well... the weak.]

... Do my powers interest you?