Board Thread:Theories and Speculation/@comment-27717552-20160513151229/@comment-26369387-20160513170804

Well, looking at how Kakashi creates Rasengan, by holding right arm with his left hand, I'm not sure if even regular Rasengan is easy for Kakashi. Then again, Kakashi has transplanted Sharingan, so it may screw things a bit...

As for Minato, it's possible that Minato could have applied Nature Transformation into Rasengan eventually, had he stayed alive. It did took him about 3 years to create Rasengan, after all.

And then there's Jiraiya(kinda forgot about him), who also learned Rasengan, but didn't add Nature Transformation into Rasengan. For this one... All I can think is that maintaining his spy network and... "research"... for his Icha Icha-books took his time.