Idea By Stubborn Donkey..Minato's Plan
Minato was a genius, and I am not talking just shinobi wise. That was stated by many characters. Maybe he knew about Madara and his plans, maybe he realized Madara would attack at Naruto's birth, maybe he knew he would have to "sacrifice" his life to put the Kyuubi into Naruto, maybe he knew jiraiya would eventually teach him, and teach him rasengan. Maybe he knew about the Kyuubi limitation shit. He knew Naruto would eventually learn to control the Kyuubi. We know he put himself into Naruto.
Like Killerbee said, its like rasengan was created for Kyuubi Naruto. Maybe it was. Maybe when the Kyuubi drains down Naruto's chakra, Minato will come in drain the rest and take control of Naruto.
What he will do then, be evil, be good, who knows?
this made so much sense to me i had to make it a topic....good one Stubborn!!