[His hand twitches a bit; the movement is odd and involuntary, like he doesn't realize he's doing it, his fingers settling against that metal band at his waist with the glowing heart at the center.]

Well...mine's a bit different - a lot of things about me are. But monsters' souls are colorless, while humans' have some sort of shade to them - they're usually very vibrant. They can change colors sometimes, too, depending on what's happening around them.

They're heart-shaped; monsters' point upwards, humans' are the opposite.