You'll get no argument from me. It's natural, as far as I know. They have some of these abilities as soon as they hatch and learn others through training. They all have some kind of affinity, just like Reason magic does.

[He turns the Gear so that Lysithea can see what looks like a piece of fruit--a mangosteen, though Felix doesn't know what that is--sitting on the windowsill on the other side of the hotel room.]

Hey, Inda. Turn around.

[...and then the fruit gets up on its tiny, stubby little legs and turns around to smile widely at the Gear.]

Her affinity is with grass. Sylvain hatched her from an egg.