Ok, be a bit clearer and more specific. Are you saying, that the weapon appears as a pick up? but once collected it's not visible?
If this is the case, you need to copy the keenblade with a gunspec,hud,vweap,and all that jazz to gamecore/guns/user/keenblade or whatever. And then make sure the keenblade.FPE in the entity bank references the gamecore/guns/ location of the keenblade, in it's "isweapon" field
if you give me some more details, like where you installed things I'll be able to help you better.
"Guns for show, knives for a pro."