User blog comment:Omega natsu2/Chapter 372: Breach, Predictions./@comment-33019320-20140219094024/@comment-4800978-20140219233509

Nick, the whole point of the Rasengan is that it is self-sustaining once complete. No contradiction has been made. From the very beginning it has been said that the Rasengan only needs a fixed amount of chakra to form, which is why it is superior to the Chidori which requires a constant flow of chakra to keep it active.