Nina's skin worked like a mirror for magic. Any spell or mana that hits it reflects away. From what Arad knew about the Tarrasque, that thing was supposed to be able to fling spells back at its caster. But Nina seems to be a bit different; if she wants to send the spells back at the caster, she needs to angle her body right, as if trying to reflect light back at its source with a mirror.
The skin seemed to be able to reflect any kind of magic and work on its own. Nina can't be healed or buffed by anyone, which seems to be the flaw of her skin. She can't pick and choose.
By the time Arad finished inspecting her skin, Nina was already about to finish eating the third arm. With the first one, her muscles evolved, and with the second, her bones, the third one seemed to harden some of her organs.
