A black slime

When the smoke vanished, there was a pile of black slime on the seal. It confused Naruto to see it. Reaching forward, he touched it with his finger. The moment he made contact, the slime grabbed his finger and began spreading across his arm. He screamed in fright, alerting the two Chunin ninjas of his location. Luckily, It was Iruka that arrived first, but what he found, almost stopped his heart. Naruto was fighting with a black mass that seemed to be trying to cover his entire body, unfortunately, there didn't seem to be much Naruto could do, as the mass covered the last inch of his head.

(Inside Naruto's mind...)
Naruto was lying on the ground. He could hear the sound of water dripping onto the ground, but it didn't sound like it should. Looking up, he found himself inside a large sewer.

"Where the hell are we" he said, not even noticing the fact he said "we" and not "I."

"You are in your own mind," a large booming voice said behind him, Naruto immediately turned around and found himself staring at a large cell door. Inside was complete darkness, except for two blood reg eyes.

"You're the Nine-tails," Naruto said, stepping forward, "Aren't you?"

"Of course. Now stop talking, I'm trying to enjoy the show."

"What show?" Naruto asks, turning around to see, what looked like a large cinema screen, with the scroll of seals still on the ground in the forest.

(Meanwhile, in the real world...)

Iruka was walking towards Naruto. The black mass had completely enveloped his body. The closer he got, the more he could see. Like the fact that Naruto was now bigger, both in height and muscle mass and there was a large white spider on his back. Before he could take another step, he heard Mizuki jump out of the trees. Turning towards him, he saw the man with a large shuriken spinning in his hand. Iruka moved before he could throw it and placed himself in front of the weapon, taking it in his back. He was standing over the new form of Naruto and saw that the black mass had, somehow, become a suit. Coughing up blood, Naruto stirred as he felt the warm liquid on his back.

"Iruka-sensei," Naruto said, but his voice was different, almost as if two people were talking at one. He could recognize the voice of Naruto, but the second one, he didn't know, "You risked your life for us."

"Of course," he said, with a sincere smile, "What Mizuki said was a lie. You are not the Nine-tails, you are Naruto Uzumaki, a citizen of the Leaf Village and one day, you "WILL" become the greatest Hokage of them all."

"How touching," Mizuki said, smirking, "At least you got that off of your cheat before I killed you."

The moment he said this, Naruto stood up. Iruka gasped as he saw how much the mass had made him grow. At first he was only about five foot four, but now he was just under six feet.

Naruto turned around and faced Mizuki. The gasps from the two Chunin were loud and full of fear. Naruto had indeed changed. The white spider symbol on his back was connected to the same symbol on his front, but his face was horrific. The people of the Leaf Village had called him a demon for his entire life, but now he actually looked the part. There were two white, almost triangular, shapes, over his eyes. His mouth was the thing that made him look like a demon. It was filled with long, sharp teeth, and a tongue hung out that was over a foot in length.

"Naruto," Iruka finally said, "What happened to you?"

"We are not Naruto," the creature said, "Naruto is inside our mind until the transformation is complete. We are Venom."

"You see Iruka," Mizuki yelled, "He is a monster. When the village hears about you, they will call for your ****."

Venom let out a laugh, it was filled with an insanity that no-one could know. Mizuki gulped as he heard it. He knew that he wasn't going to survive this encounter. Whatever Venom was, he wouldn't think twice about killing him, "You have tried to kill us and our sensei. For that you will not be walking away from this," Venom raised his fist and a black substance shot out and clung to Mizuki. He was unable to brake free from Venom. Even his arms were stuck to his chest. Venom pulled on the line and Mizuki flew towards him, traveling over thirty feet, before landing right in front of the monster.

Venom grabbed Mizuki by the throat and lifted him up into the air. Both Iruka and Mizuki where stunned at the strength he was showing. He then slammed the Chunin to the ground and began to, repeatedly smash his fist into his face. If that wasn't enough, Venom grabbed him by the arms and slowly began to tear them off. Mizuki's screams of pain were like music to his ears and he just laughed at his torment, but Venom wasn't the only one enjoying it. Inside of Naruto's mind, the Nine-tails was salivating at sheer amount of blood coming from Mizuki.

(Inside Naruto's mind...)

"I like him," the Nine-tails stated, "His blood-lust, almost, rivals my own."

"We're glad you think that," Venom says, appearing before both him and Naruto, "We are sorry for taking over your body like this, but your father promised us you would be our host and before you ask, he swore us to secrecy, regarding his identity," turning towards the fox, "You like the blood of the the fallen, but as you are sealed inside of this boy, you cannot feel it anymore. What if we made a deal? You help us, by giving Naruto some of your power when he needs it and we'll make him one of the most feared creatures alive. Though, not as feared as you of course."

"It's a deal," the fox says, giggling like a schoolgirl. She turned to Naruto and saw the look of confusion on his face, "You read what was on the note."

The read eyes of the fox disappeared and a woman walked out of the darkness. She was absolutely beautiful. She was a bit taller than Naruto and had bright orange hair, blood red eyes and nine fox tails, just above her well sculpted ass. Naruto fainted, the moment he saw her. Blood spurting out his nose. The Nine-tails was completely naked, showing her large E-cup breasts and a small patch of orange hair, just above her pussy. She giggled again at Naruto's actions and looked back up to Venom, "I've been waiting eighteen years to do that. My last vessel was female, so I couldn't have as much fun."

(Back to Mizuki...)

Venom had dropped Mizuki to the floor again. His arms were lying beside him, blood spurting out of the stumps left behind.

"We think we should be a little merciful to you and end you life quickly," Venom said, with his insane chuckle.

Grabbing Mizuki's head and legs, Venom ripped the Chunin in half, killing him. Turning back to Iruka, the suit began to recede, the living mask was quickly replaced by Naruto's face. Looking down, he found himself wearing his usual clothes, except they were black and there was a white spider on the front. Looking at his back, he noticed the red spiral was gone, but his clothes shifted, and it appeared.

"We can become any type of clothing you want us to be," Venom said in his thoughts.

"Are you alright?" Naruto asks.

"I'm fine," he grunted, "but what was that?"

"I'll explain later," a large grin spread across Naruto's face, "Have I graduated?"

"What?" Iruka asks.

"I can do a clone jutsu now," Naruto says, using the first two fingers of both hands to make a cross, "Watch. Shadow-clone Jutsu!"

In a poof of white smoke, two more Naruto's appeared in front of Iruka and picked him up. The Chunin just smiled and told Naruto to close his eyes. When he opened them again, he saw Iruka holding his green goggles. Reaching up to his head, he found a ninja headband.

"Congratulations Naruto," Iruka says, "You graduate. Now can you help me get to the hospital. Then I want you to go see the Hokage. He has probably witnessed everything already, so you should explain yourself to him."

Naruto jumped into the air as his clones jumped into the trees, making a leap, that even a Jounin would have some trouble with.