It's an original jutsu by Ryun, expanding on the original concept for the Rasengan by the Fourth Hokage's and Naruto's ideals: mixing ones chakra element with the Rasengan. However, this was proven to be the most difficult thing to do. Luke even explained to him that, adding someones chakra element with the Rasengan, takes an incredible amount of skill or rather natural talent or sense. Ryun mixed his lightning element, maintaining its original stability and increasing its power, far beyond that of his Water Release: Rasengan. Another example of the power of the jutsu is shown when it was tested against Luke's Fire Release: Rasengan. Ryun needs only his own two hands. Hayai Sarutobi later learned this technique by himself, using one shadow clone to add Lighting element to his Rasengan.