Sun God gave his baby Karna "armor and earrings" — an Older Than Earth artifact fished out of the primal Chaos. This gift was irremovable by any means accessible to mortals, made him highly resistant to both normal damage and "Celestial Weapons", but didn't impair in any way his growth from baby to impressive warrior. The earrings — with gem(s)? — gave Karna his name, but the armor is mentioned only when he needs it. On the warriors' tournament, it was "hey, who's that guy in cool armor?", but people on streets or in his stepfather's stables didn't gawk at a strange boy always walking around wrapped in shiny metal for no apparent reason and didn't spread rumors through all the lands. Karna was considered the single most dangerous man on the whole battlefield, even though there were a few absurdly powerful mentors on the same side, and several other godlings and one avatar of a deity on another; Indra thought other guys (otherwise the best warriors ever) still has no chance to bring down Karna until he managed to remove this artifact. The armor-and-earrings ("kavach kundal") were found, given, and removed always together, as two parts of one thing. Does This Remind You of Anything? already?
If these eggshells had nutritional value, it would be considered a way of caring for their young, much like mammals with their milk. Why not combine the two? There is a layer of subcutaneous fat cells just under what we call the skin. These fat cells, normally excellent at storing extra calories, could secrete nutrients into the skin just as it is being shed. The mother builds up a layer of "baby fat," goes off to lay her egg(s) and sheds a few layers of skin rather than leaving her offspring to hunt.
If she goes back to a steady den, she already has she several layers to use as "nesting material." However, a more vulnerable creature, chased from nest to nest, requires the ability to shed "intentionally." Besides not being caught without a protective outer layer, being able to shed intentionally has other benefits. Think "winter coat" and "summer coat."
If you're familiar with mammals, you might think of the thicker fur grown by cats and dogs in the winter. That's one reason they shed hair all over your furniture. Now, some reptiles hibernate; you can see why they would want warm, thick skins for the winter.
But you might not immediately see what comes before this. Before hibernating, the animal must build up a thick layer of fat, which means they must eat a lot. This applies as much to bears as it does to alligators, and you know what kinds of things bears and alligators eat. Summer would be this reptile's mating season, where the strongest males battle for mates; fall to early winter is when the female sheds her mating plumage to become a true killing machine.
You've heard about those species where the female eats her mate. The way the Witchblade seems to selectively cover the host body's erogenous zones (nipples, etcetera) suggests that the symbiote has a potent hormone cocktail in its arsenal. S&M claims that during some states of arousal, pain and violence become pleasurable. Hopped up on the right kind of stimulation, even a normal human could appear unnaturally strong. This is not to say that the witchblade is steroid-free.
So far we have an Evil Hand skin graft from an alien reptile (if you're into scifi) or a dragon (if you're into fantasy). Only not quite. Remember that whatever reptile we're talking is planning to shed several layers of skin in the next few months, most of them soon after the baby hatches. It would be helpful if they could grow several layers of skin UNDERNEATH their armored outer layer. This layer is also being supplied with nutrients to make sure it's a viable source of food later. Toss in a functioning neural net, and we have a symbiotic lifeform. The rate at which the Witchblade grows borders on the cancerous. Some mothers might put primitive brain cells into their babies' diet to ensure the babies are smarter and better able to survive.
This is the organic model. The Witchblade as it appears in the series is a several-hundred-year old relic, similar to an ancient bonsai tree that's been handed down for generations. It implies careful cultivation, if not fabrication, and it can't be compared to the original any more than a trained attack dog should be compared to the pack of wolves that generally shies away from humans.
So in spring, the female reptile blossoms in a layer of mating plumage, watches the males fight over her all summer, then settles down with the victor in early fall. After every egg is laid in its nest, the female sheds her sweet smelling bridal veil and grows something similar to what we call a witchblade. The symbiotic armor covers the sensitive areas of her body and perverts the mating instinct into an appetite for wanton destruction, which produces large quantities of dead animal meat. She eats the meat and grows fat before returning to her nest for the winter. Once settled in, she sheds her armor and returns to normal to ensure that she doesn't harm the nestlings. Once the babies hatch, they will eat their eggs and then the shed skin. The latent "ferocity" encourages the young to develop "killer instinct." In some species, the young are born in large clutches of eggs, but then fight and kill each other until only a few, particularly strong specimens remain. This could be the case here, or perhaps the "savagery of the skin" requires a particular trigger to activate, a mixture of adrenaline and sex hormones. In either case, the armor, while hard, is made of compounds that easily dissolve in the baby's stomach. The are able to absorb the nutrients and even some of the "instinct" contained in the primitive braincells. (Perhaps the symbiote layer is synthesized from the dead mate, but that sort of squick is a Poison Oak Epileptic Trees.) Anyway, the biochemistry is simple enough to be almost universal. With the right host, the skin can even be employed by a member of a different species.
- The most compelling biological reason to return a host into its normal shape is that otherwise, its species won't recognize it and this could gradually breed out the best potential host traits out of the species, which is self-destructive. Conversely, stimulation (in sensible limits) of a chosen host's reproductive behaviour means spreading all traits that make better hosts.
You are a sentient (sort of) defensive symbiont — it's your main purpose in this life — stranded among potential-host species but not understanding them well. Attempts at telepathic communications have mixed results — they aren't adapted to this and the only sure thing is "its mind is a mess". They are rather violent, and you suspect many are downright insane; but you still have no way to judge. Your few peers are in the same trouble and have wildly different ideas about the situation. Now, the task is to get good hosts to join, without harming the whole species by counter-natural choice (one just doesn't do this to the species one depends upon). What to do? The species in question reproduces sexually and, as such, supposedly are able to select what is good to keep. And you are a good tele-empath, so when there's no clue for a choice, use their own instincts: watch reactions of their kind, see any correlations, react accordingly. Simple enough. This may be intentional or instinctive, but the result is the same. If the host species happen to be Homo sapiens sapiens, this approach easily leads to the conclusion: aggressive females with outstanding hormonal balance and corresponding figure are the best hosts to protect, and they always need some action.
- There was also a late-canonical theory about "Male Gaze" of Witchblade, but it has holes. It's not clear what they could find in creatures so absurdly different... and if so, the symbiont isn't outside to ogle its host to begin with.