Project EF-12 is an 'engine' / customizable game created by Quad Arrow. It was marketed around Western fighting game circles as a '3D MUGEN', an engine that allows you to create and modify a fighting game with 2D fighters.
One of the biggest draws of MUGEN was the ability to download created fighters and stages, quickly making way for an 'everything vs. everything' scene.
However, EF-12 suffered from a fatal flaw - age. The primary tool for creation of EF-12 assets was Softimage Mod Tool, which has been long deprecated. There exists a Blender plugin, but it was left in an unfinished state and only partially functions and has limited documentation.
So, with EF-12's EOL announced in 2021, it is now officially abandonware.
There is no official support and up-to-date official docs are all in Japanese.