There was a project a few years ago where 2 or 3 guys were going to redo certain animations. I'm pretty sure they did half of 1 and quit. The only feasible way to create animations is to make an import export tool.
Borde tried to make a COLLADA one but eventually gave up. Really, your best bet is to figure out how to substitute Galian Beast's animations over Red's. Either way good luck
I myself have done several 100% animation changes, ranging from making Tifa have archer animations, (She held her right hand out, pulled the other one back and shot the (invisible) arrow with variants of it to allow for a bow) making tifa have a sword, (this took forever to work right.) making Cloud have the exact animations of the other soldiers, making a unique swordsman animation set (For a character in one of my projects, he moves like a combination between Reno, Cid and Squall.) among others.
One thing I tried was making Nanaki use a sword, which involved it staying in a scabbard on his back, and he pulled it out for attacks, I spent 3 weeks solid trying that, but Nanaki has the most complicated animation structure out of everyone, and by comparison, it's a cakewalk to do the entirety of Cloud, which is the simplistic.
If you are genuinely going to try to make Nanaki stand out on 2 legs with his native animations, you will spend months or possibly years doing this, it would be best to make him more into Kimahri from Final Fantasy X, and his limits could be changed into more generic things.