Disclaimer: If I owned the Naruto series, Kakashi, Itachi, and Gaara would all be immortal. Since that doesn't seem to be the case, it's safe to conclude that I don't own it.
Warning: This story contains spoilers for the manga.
Masks
The first thought that ran through every Akatsuki member's mind on the day they met Tobi was, "What the hell is with that stupid mask?" ANBU members wore masks to conceal their identities—they often went on assassination missions, and didn't want friends or relatives of the target to get a look at their face and track them down later on some futile quest for revenge. Ninjas with advanced bloodlines often wore masks to conceal distinctive facial features that would reveal the nature of their abilities to their enemies—or simply to hide the traits that made them different from everyone else. Some shinobi chose to wear masks because they felt that hiding their faces made them look more intimidating to their opponents. But in all these cases, the masks they wore were intended to be fearsome, stoic, or at least dignified. Certainly no ninja would be caught dead wearing a bright orange mask with a black swirling pattern surrounding the eyehole.
The Akatsuki also found it odd that Tobi wore his mask all the time. Sure, they all buttoned up the high collars of their cloaks and wore face-concealing hats when they were in a village. But that was just so they wouldn't have to deal with the annoyance of fighting off hordes of chuunin who caught a glimpse of their face and somehow decided that fighting Uchiha Itachi (or whoever) was a good idea. When they were in the company of other members, with no enemy shinobi or civilians around, they took off the hats and unbuttoned their cloaks. There was no reason to hide their faces from each other. A man with blue skin and gills, or a face that was stitched together, or a face that was half black and half white, would stand out in a crowd of ordinary people. But there was no reason to hide your physical abnormality when most of your comrades were just as abnormal as you were.
What the other Akatsuki members failed to realize was that all of them were wearing masks—just masks of a different sort from the one Tobi displayed.
Someone might say that Sasori's mask is Hiruko, the shell in which he hides himself. But that person would be wrong. Sasori's mask is not Hiruko. Sasori's mask is his own puppet body. It's the innocent, childlike, honest face that hides a bitter and jaded shinobi who wants to live forever even though he doesn't really have anything to live for.
Hidan's mask is his fanaticism. His unswerving and loudly proclaimed devotion to Jashin makes everyone believe that he is confident in his faith. But behind Hidan's mask of zealotry is a deep and unspeakable fear. The fear that his immortality isn't a gift from his god, but only an advanced bloodline achieved through entirely natural means. The fear that there is no omnipotent being watching over all humanity and dictating the boundaries of virtue and sin in clear, uncompromising terms. The fear that if and when he finally does die, he will not rise to eternal glory at Jashin's side, but only fade away into oblivion.
Kakuzu's mask is his greed. He works tirelessly to accumulate money, or precious objects that he could someday sell for money. He keeps a meticulous list of all his income and expenses, constantly devising new ways to maximize one and minimize the other. But his continuous pursuit of wealth masks a gaping emptiness: money is all Kakuzu cares about because money is all Kakuzu has. He has no family to cherish, no friends to care for, no comrades to protect (he doesn't really see the Akatsuki as comrades, just as a means to the end of obtaining still more money), no loyalties to uphold. He pours more and more money into the hole in his spirit, but somehow it never seems to be filled.
Tobi has another mask besides the one that covers his face. That mask is his cheerful stupidity. His childlike nature makes him seem like he's always delighted with everything around him. But that ebullience exists only on the surface. Beneath it, Tobi is terrified, because he has no idea who he is. He remembers lying under a pile of rocks, and being rescued from certain death by Zetsu. But he has no memory of how he came to be under that pile of rocks, nor of his life before that point. He laughs and jokes and acts like an idiot because he desperately hopes that no one else will notice how much this frightens him.
Deidara's mask is the joy he finds in destruction. Every person he's ever loved has either left him or died, and everything he ever cherished has been destroyed. And so, if he finds something beautiful or believes that he's starting to care about it, he cheerfully demolishes it. Deep down, he's terribly saddened by the conviction that nothing good can last, and he destroys everything that he loves before it can be taken away from him. That way, at least he's prepared for the loss.
Zetsu's mask is his split personality. Most of the time, he doesn't even like to fight—he's content to observe from a distance, to convey information without having to harm anyone. But there's always a dark undercurrent in his mind, a ravenous, greedy voice that urges him to tear flesh and crack bones between his teeth. This part of him horrifies him, and so he has tried to distance himself from it—tried so hard that it finally split off into a separate personality, one that shares his body but not his mind. That division is a mask, hiding the fact that the brutal, merciless killer is part of him too.
Itachi's mask is his unceasing stoicism. He shows no emotion in the face of either joy or tragedy. The expression on his face remains exactly the same whether he has just triumphed in battle or seen a comrade fall. But as with his kinsman Tobi, this mask serves to conceal an overwhelming dread. For Itachi, it's the fear that all he has done will be in vain. The destruction of his clan, the way he's tried to shape Sasuke into a ruthless avenger…his worst fear is that the plan he's been crafting for years will suddenly fall apart.
The blue-haired kunoichi's mask is her silence. She speaks even more rarely than Itachi does. To speak is to reveal something of oneself, to expose one's feelings and hopes and desires and fears to others. When she lived in her home village, she was almost as talkative as Naruto—but the repayment she received for opening herself up in this way was betrayal. The other Akatsuki members believe that she remains silent because she feels contempt for them, as if they were not worth the effort of speaking to them. In truth, she remains silent because she trusts no one, and does not wish to make herself vulnerable by giving others a glimpse into her mind.
Kisame's mask is his seemingly carefree bloodlust. He loves to fight and will take any opportunity to do so. That's the way the Mist Village taught him that a shinobi should act. Kisame embraced that teaching wholeheartedly, even killing his best friend during the Mist's notorious Academy graduation exam. But every so often, he wonders if all the things he learned in the Mist were really true. After all, he has already decided that some parts of their system are fatally flawed—that's why he tried to assassinate the Daimyo, the crime for which he was designated an S-rank outlaw. But if some parts of the Mist's system are flawed, isn't it also possible that the very foundation of their beliefs—the foundation on which he's built his entire life, even after leaving his home—is also erroneous? And if that's true, how is he supposed to live his life? He throws himself into battle with abandon, because the adrenaline rush and the basic instinct of a fight-or-flight situation keeps these questions at bay.
Even the Leader wears a mask. His mask is his anonymity. No one in the Akatsuki has ever seen his face, and no one knows his name. He is a mystery even to his followers. That mystery hides a deep pain that he allows no one else to see. It is the pain of a man who longs for his home, but knows that he can never return there.
Everyone has secrets. As a general rule, shinobi have more secrets—and bigger ones—than civilians do. But even among shinobi, the Akatsuki members have more secrets than most. And although only one of them hides his face behind a mask, all of them hide their secrets.
A/N: See, I'm not dead! I just haven't posted anything in a while because I've been really busy. The idea for this fic randomly popped into my head last night, and I wrote it down. It figures—I've been working on a Shikamaru fic for a week, and a SasoDei story for a month (a month!) and can't seem to get either finished, but then I get a random, completely unrelated idea for a story and finish it in two days. Anyway, I rather like how this turned out, and I hope you enjoy it too.