Nega-Xehanort is the SAFA Xehanort who ended up becoming a darker and more evil variant of the original Xehanort because of the events of Kingdom Hearts III deviating from what was thought of him before KH3, being created by Cobra and Architect from a time spell after seeing the original Xehanort unworthy for his less-sinister new outlook. Thing is, Nega-Xehanort is not nessersarly an entirely unigte creation of their's. Nega-Xehanort is actselly an inadvertently revived endling of a virtually extinct Destructor Class race of Outer Gods, refered to originally as "Omni-Hearts", which were basicly the mega kings of all the creatures of the outer realm of Kingdom Hearts. At most, they were basicly bigger versons of Erasers, but were pre-requisits in the days before The Xexaxez were created. The Amoral Ones originally wanted to utilised Kingdom Hearts as a means to circumvent Interdimentional Empires, via the Omni-Hearts would use the power against such. However, the Omni-Hearts ended up dooming themselves when they invented a method that even the entire Outer God forces had feared: the Great Cycle. The Outer Gods fear this ability would be riped for abuse and that messing with Kingdom Hearts was a msitake, thus, effective quickly, the Outer Gods destroyed the Omni-Hearts to the last member, and swore to be more respectful to Kingdom Hearts there on out. But now, the aptly named Nega-Xehanort was inadvertingly revived and considered a clone to the original Xehanort meant to be an evil dopplerganger. As a resort, having gained the book of predictions, Nega-Xehanort plotted to subugate the entire United Universes to the Great Cycle, simply as personal payback to spite the outer gods for the destruction of the Omni-Hearts. Nega-Xehanort's true form is a fuzed mix of the intended Xehanort clone and that of a semblence of what an Omni-Heart had looked like.