Um...

Let's review Kingdom Hearts Organization Member weapons shall we?

Axel - Chakrams? There's another word, but this is the only thing I can think of right now.

Lexaeus - Giant tomohawk...

Marluxia - Scythe

Vexen - Stabbity stab stab shield

Larxene - Darts/Knives

Zexion - Unknown. He does try to manipulate his victims though.

Xaldin - A bunch of spears....

And finally, we reach the new character, Demix. See him on Kingdom Hearts Ultimania, or Gerbil's site, it's on the side. So what does he have? Well...it LOOKS like a....

Guitar.

Um...