On this link we shall finally learn THE TRUTH!!!

http://en.wikipedia.org/wiki/Organization_XIII

Go down to Zexion and it tells us...

1. He uses his element of illusion to make copies of himself and of his opponents weapon (this explains why he wielded Soul Eater)

2. His weapon is a BOOK and he attacks with a flurry of pages or traps victims in it.

THANKYOU WIKIPEDIA!!!