Unlike the revived Koei style, Niko style has a complete system with extensive techniques, so there's no way it was created by one man in a single lifetime. There must be an origin somewhere, and Niko improved / modernized it to make his own style. Setsuna can learn from a practitioner of old style, or someone who created it together with Niko.
Anyway, people sure like to use "asspull". Is it trendy?