Naruto did a shadow clone jutsu. The real Naruto held out a rubber ball while the clone hit it in several different places. He stood there holding it out, it didn't move. "This is the final step." he said.
"I don't get it nya." said Jen.
"Oh, yeah, neither did I when I learned. Maybe this'll clear things up." said Naruto. The clone did the same thing to the other hand. A small ball of rapidly spinning chakra formed.
"Oh, I get it nya! So that ball of chakra is also in the rubber ball nya." said Jen.
"Yep. As soon as you can get a ball to not even budge when spinning chakra inside, you'll have mastered the jutsu." said Naruto.
"What's so special about it anyways nya?" asked Jen. She looked dissappointed.
"What you've learned so far does this." said Naruto. The ball of chakra got bigger and unstable. He slammed it into the ground and the ball vanished due to the shock. It made a shallow crater with a swirl design in it.
"Cool nya." said Jen.
"Here's what the real thing does." said Naruto. The rubber ball burst reavealing the more stable ball of chakra within. He turned away from the crater a little facing undamaged ground. Then he slammed the ball of chakra into the ground. The ball remained stable while making a deeper and wider crater with a swirl design in it. The ball of chakra vanished. "And that time I made the jutsu diminish on purpose. What'cha think of the Rasengan?" asked Naruto.
"Gimme that ball nya!" said Jen. She grabbed a rubber ball out of the backpack and tried to do the jutsu. The ball popped. "Crap! It popped nya."
"Don't get your hopes up little lady." said Jiraiya. "Naruto mastered this jutsu when he did because his life depended on it. It took the inventor of the Rasengan, the Fourth Hokage, 3 years to master it. Just because Naruto only needed a week doesn't mean you only need a week."
"Oh yeah nya?! I'll beat that record, you just watch me nya!" said Jen.
"Yeah, if you do that," said Jiraiya "I'll personally make sure you're promoted to Chunin. I doubt you'll do it though."
"It's a bet then nya." said Jen. "Oh God! I think I'm about to change again nya!"