Carnage
The next morning, Naruto awoke in a sewer covered with red-and-black webs.
A mirror image of him appeared, before being covered in the 'suit'.
It said, "You'll have a number of questions, so go ahead and start asking."
The boy stammered out, "Where am I? Who—no, WHAT are you?!"
"This is your mind. And I am an alien symbiote—a creature that survives by bonding with a host; namely: you."
Stepping back, Naruto accused, "What, you're going to eat me from the inside?!"
"No, but others of my race do that. I, through you, absorb energy from other people in order to survive. But… it's a two-way street."
Caught off guard, Naruto asked, "How so?"
The creature seemed to grin as it told him, "You'll find that out when you wake up."
Having about half an hour of free time, the symbiote's voice told Naruto, "Because of our bond, you're several times stronger, faster, and tougher than any ordinary human being. My first host, Cletus Kasady, was able to life about fifty tons straight off the ground."
'How much is fifty tons?'
"Imagine a solid rock the size of your apartment—that's roughly five tons."
Jumping around the Forest of Death, Naruto began learning to use his strength. Punching a rather thick tree with all of his might when the suit covered him, the monolithic plant toppled over, split clean in two at the base.
That night, Naruto gave up sleep and let the symbiote costume engulf him once more.
"I suppose I need a name we can use… why go against the classics? My name is Carnage now."
Carnage (as Naruto will be called when wearing the suit) started learning more about his powers. Strength, speed, agility, the power to stick to walls, having the symbiote make disguises—all this and more he began to learn.
He also found that he could use the symbiote to form tendrils with which to attack from a distance, whether by hardening them like spears, flailing them like whips, or creating blades on the ends like a scythe on a chain.
"We also have cosmic powers, from when I temporarily bonded with Norrin Radd, better known as the Silver Surfer. However, we can't use them too frequently, as they're very exhausting. We even have two other senses: Spider-Sense, which is warns us of danger, and a Symbiote-sense with which we can detect other symbiotes in the vicinity. Combined, these two additional senses can be used much like a radar."
Entering the Village proper, Carnage wondered, "I'm hungry, but it's not like any hunger I've ever felt before. What is it?"
"Symbiotes normally feed off of the host I'm bonded with, but my… progenitor and I do not. Neither does my descendant. But since we don't feed on our hosts, we have to feed on OTHER people using our hosts as a medium."
"So I have to eat people?!"
"No; by coming into contact with the symbiote, their life energy—including what you call chakra—is absorbed via a type of osmosis. Absorbing their energy is how we survive. Because of our bond, if either of us dies, then so will the other."
Not happy about it, but bereft of any alternatives, Carnage resumed leaping across the rooftops. "If I have to… feed on other people, then I'll only attack the ones that deserve it: only criminals, no innocents."
Unbeknownst to Naruto, he had basically adopted a philosophy similar to what Carnage's 'Father', Venom had.
At any rate, feeding on criminals shouldn't be too difficult; the entire police force had been killed off about a year ago, and the civilian sections of the city were caught up in a gang war.
Every few seconds, Carnage let out a combined pulse of Spider-sense and Symbiote-sense, looking not only for—he couldn't bring himself to think 'food'—prey, but also for any potential threats.
After a few moments, he observed a robbery in progress: three men holding up a convenience store. Choosing to end it quickly, Carnage tapped one of them and sent him flying about thirty feet away, having absorbed minimal energy from the brief contact.
Turning his arm into a massive spear, Carnage impaled the next one, and then caused it to branch out like tree roots, before spikes finally came out of nearly every part of his opponent's body.
This time, he'd taken almost all of the life energy. Facing the final burglar, Carnage formed six spikes from the symbiote and hurled them at him, instantly killing him and draining most of his energy.
Making sure to take the rest of the energy from the three thieves, Carnage leapt into the shadows, dissolved, and then fled into the sewers.
All of this had occurred in just a matter of seconds.
And there was virtually no evidence as to what, exactly, had done this. Of course, had they known about Carnage, he'd be the only suspect, but they didn't yet, so the cause of the deaths—as far as the authorities were concerned—was a complete enigma.
And there hadn't been any witnesses, either.
Carnage faced a rather singular conflict: although he was a bit horrified that he'd killed those people—and even more so because he'd actually enjoyed doing it—he was also savagely thrilled t being able to get away with it.
By dawn, Carnage had 'reverted' to Naruto, and actually looked rather well-rested.
Settling in for another day of the usual, Naruto morphed the 'suit' into black cargo pants, a bloodred t-shirt, and dark red sneakers. Deciding that something was missing, he added a black tribal pattern on the shirt, and also formed a black long-sleeved jacket that went halfway down to his knees, but left it unzipped. It felt a lot like fleece.
Grabbing his books and pack, noting to store them in the symbiote later (supposedly, it was like having infinite-sized pockets), he calmly walked towards the Academy.
Author's Notes: for symbiote powers and Spider-Sense, I'm using a combination of concepts from Spider-Man: Web of Shadows (PS3), Spider-Man: Friend or Foe (PS2), the comic books, and the Marvel Database project (a Wiki for ALL Marvel Comics). The original written chapter for this was a lot shorter, probably a page less. Now where's that question some of you are just dying to ask: "If Carnage has to feed on people, then why not take energy from the Kyuubi?"
Well, for starters, Demon energy would be way more powerful than human energy, so if Carnage WERE to feed off the Kyuubi, then obviously he wouldn't have to feed on humans anymore. BUT the only energy he'd be able to take is chakra, which is a significant part of life energy, as I define it in this story, but NOT all of it. If you've read any of the Twilight books, it would be a similar concept to Carlisle or any of the other Cullens drinking animal blood in order to keep themselves strong enough to resist the allure of human blood. Furthermore, Naruto doesn't know about the Kyuubi yet, and the symbiote hasn't really seen fit to tell him; even if it had, the idea of absorbing Demon chakra hasn't occurred to either of them yet.