Okay, this worked pretty well overall, but there's a few issues that remain.
Firstly, a random Masamune appears arbitrarily during any of Sephiroth's animation at a weird location. I think it's always a bit below the blade, as in the direction the blade is curved in. It doesn't appear in Kimera and I don't really know why this happens. I could deal with it, but it just looks ugly.
Secondly, animations work great. But there's one little issue that's left. I'd like it if Sephiroth had the Octaslash ability. For that one, I used Big Brawl as base. Now for one, I tried all animations on the list and the spellcasting ones are the ones that work... kind of. Sephiroth of course teleports all over the place, hits 8 times, and then stays at an arbitrary spot. Problem is for one, he doesn't move back to his original spot, two, if I try to have him do it twice, the "smoke" animation of Big Brawl is still played but Sephiroth doesn't teleport and hit people and there are no damage figures. It only works again if I completely reset FF7.