Disclaimer: Naruto belongs to Masashi Kishimoto. If it didn't, this would probably have been the actual ending.
Just so you know, this takes place after chapter 574 of the manga.
Naruto, after defeating the other tailed beasts, was truly exhausted, when, out of the blue, Tobi came and attacked him. The attack was about the hit Naruto when it was stopped by the guy who runs the Ichiraku Ramen Shop.
"What?" Naruto shouted.
"Naruto, there's something I have to tell you." The man said. "The reason that we were the only people in the Leaf to accept you when no one else did was because I am a secret descendent of the Senju clan, and I'm here to teach you how to use the Rinnegan." He took out a bowl of steaming hot noodles. "Here, eat this, and the power of the Rinnegan becomes yours."
"It's that simple?" Naruto asked, bewildered.
"Simple!" Tobi shouted. "It took me years to figure out that recipe!"
Meanwhile, Itachi caught up with Sasuke. They were about to fight when Itachi pulled out something from his sleeve.
"Is that…" Sasuke wondered.
"Yes. It's the teddy bear that you loved when you were a child." Itachi said.
"Wow. That somehow has managed to make me forget all of my desire for revenge. I think I'll go help Naruto now." Sasuke said.
"I'm going to crumble to dust then." Itachi said.
Naruto, who had finished the ramen and had awakened his Rinnegan was getting ready to fight Tobi.
"That's it!" Naruto shouted. "I'm going to destroy you! You killed my father."
"No Naruto." Tobi said. "I am your father." He removed his mask to reveal that he is actually the Fourth Hokage.
"How is that possible?" Naruto asked.
"Simple. I'm actually a psychotic maniac who wants to rule the world. I kidnapped you and told all those lies to your mother and everyone else so you would grow stronger. Now, you will join me in my campaign to conquer the world!" The Fourth Hokage shouted.
"Okay then, I'll help you in your evil plan." Naruto said.
"No Naruto, you must defeat him." Sasuke said, who had just came out of nowhere.
"If Sasuke says it, it must be true." Naruto said. He then combined the power of all of the bijuu and tried to defeat Minato, but failed.
"Naruto, you must defeat him with your signature move." Sasuke told him.
"I've tried the rasengan!" Naruto complained.
"No, your true signature move, the one jutsu that you've spent years practicing, the very first one that you've ever used." Sasuke said. Naruto understood and used the Harem Jutsu, which then made Minato vanish in a puff of smoke.
"I'll join the village if I become Hokage." Sasuke said.
"Okay then." Naruto said.
"Now that I'm Hokage, I will initiate a variety of changes. Free I-pods for everyone." Sasuke said. Everyone cheered.
Sasuke then became Hokage and became the Leaf's greatest hero while Naruto was forgotten, and so everyone besides Naruto lived happily ever after. The end.