It's an original jutsu by Kyūka, expanding on the original concept for the Rasengan by her brother, the Fourth Hokage's and her nephew, Naruto's ideals: mixing ones chakra element with the Rasengan. However, this was proven to be the most difficult thing to do. Kyūka even explained that, adding someones chakra element with the Rasengan, takes an incredible amount of skill or rather natural talent or sense. Kyūka mixed her lightning element, maintaining its original stability and increasing its power, far beyond that of the regular Rasengan.