Ok, so after some tweaking, I come up with this:
This item is a little longer than a longsword, but after some tweaking, I think it should be ok with longsword VFX if you want to apply something to it. Definitely too big for the scimitar, which is currently in this character's other hand. It appears about 2x as long.
This version has 3 parts, which allowed me to better set a definite cut between the blade and the rest of the weapon. I then set the opacity on the blade to 75%, and gave it a cyan self illumination. For giggles, I also cloned the blade, inverted the normals, and removed any smoothing, which gives the weapon a back-crystal face, which is 50% transparent. Overall, it appears almost completely opague and you can't see much through it. Because I didn't set other details or make a TXI, it also doesn't display emitter particles through it correctly, nor is the blade texture additive with the surrounding textures.
All together, it does not look very special in the daylight, but you can see in a dungeon, it looks sweet!
There are still some issues with the placement of the hand cup. It doesn't actually have a real handle inside the cup, so you might apply one from the handles selection that doesn't look bad with it, if you intend to use it on invisible creatures. The texture on the cup is also crap, but I personally don't want to play with the handle anymore. Somebody else can feel free to beautify the texture.
Edit:
I've added this item to the files as longsword top appearance 9 color 2
https://www.dropbox....51/FFWeapons.7z
OR
https://www.dropbox....i/FFWeapons.zip