yes, you are missing the Celestial mirror.
You need to obtain the Cloudy Mirror from the Chocobo race in Remien Temple, then power it up at the big ugly red/orange thing in the glittery path in Macalania.
after that you can obtain the weapon. But it will be useless with "No AP", which means you have to use the Crest and Sigil to power it up the same way you powered up the Cloudy Mirror
The I is moving 
I would rather live in my own shadow...at least then I would be compared to a past I'm more familiar with ~I~
Fear me, Hate me, Curse me, for I will question your every move ~I~
My past hold much pain and loss. I will conquer it by creating the perfect future ~Ixidor the Reality Sculptor (Magic the Gathering)~
