KEYS. A keyhole rests above their heart area, sometimes specks of light reflect from the inside. Born with a key at hand they cannot unlock their own, rather it seems that it'll fit to someone else's... but who's? Each Fragilius have a crystalline heart that harbors most of their life force, moving the matter throughout their bodies.
PHYSIOLOGY. Their insides are hollow, enough to fit skeletal-like structures which like their inside, corresponds to their material. Within the bones and cavities, flow aether or nether matter which acts like blood.
DANGER. If all of the matter escapes due to x reason, the Fragilius is dead, and leaves empty vessels until it disintegrates. When a Fragilius is in trouble and susceptible to breakage or injury, multiple things can occur, which resembles human like occurrences. [ corruption ] can occur.
ANATOMY. Non-newtonian in fluid and material, meaning if they wish to be able to be touched or feel calm and safe, their limbs can sustain a lot more pressure and feel soft and squishy. Hence, Fragilius break only when they do not suspect it or feel negatively. Brittle, when caught off guard.