When I found auron's celestial weapon, I didnt know you could power them up so I added ablities too it. Now when I try to power it up with the mirror it says I dont have a celestial weapon?

You can't add abilties to celestial weapons... Chances are, you didn;t get Auron's CW; probably a different one... Cause there's Murasume and Mausume and it's confusing...

Did you get the sword at Mi'heim? If Yes, then it's Auron's CW. If not (meaning you got it from Besaid or customized it) then you didn't get it...

ah yes, I got it from besaid ruins

Here's some information from a FAQ at GameFAQs about Auron's CW:


- F. Auron's Masamune -

Weapon Location: Behind a mandala at Mushroom Rock Road. At the bottom of the
Calm Lands valley, at the opposite end of the crevasse from the Cave of the
Stolen Fayth, take the Rusty Sword (key item) from the rocky alcove. Then go
to Mushroom Rock Road and continue straight ahead north until you see a little
green square on the area map. (Recall that earlier in the game, during
Operation Mi'ihen, you were diverted to a west exit instead of allowed to
venture north.) It's the second left on the first screen of Mushroom Rock Road.
The green square represents a floating mushroom stone, ride it up to a plateau,
and stick the sword in the ground next to the statue of a warrior standing over
a slain behemoth. The mandala will appear on the wall behind you. You MUST have
the Celestial Mirror in your inventory to get the weapon.

Mars Crest location: In a chest in the old part of Mi'ihen Highroad. To get
there, go north on Mi'ihen Highroad until you reach the entrance of Mushroom
Rock Road, then hang a U-turn and go south.

Mars Sigil location: Unlock any combination of 10 Area Creations or Species
Creations bosses at the Monster Arena to the east of the Calm Lands, and the
trainer will give this to you. Area Creations are unlocked by capturing at
least one of each monster in a particular area, and Species Creations are
unlocked by capturing several of each monster from a particular species -
Bombs, Wolves, or Floating Eyeballs, for example. If this isn't descriptive
enough, see my Monster Arena FAQ for the exact conditions to unlock bosses.
And if the trainer doesn't give the Mars Sigil to you, either a) keep
chatting with him until he does, or b) you didn't unlock enough special bosses
- Original Creations do NOT count towards your total.

Difficulty to Obtain: Fairly easy, but time-consuming. You have to do a lot
of running around to get the weapon and the Crest, and unlocking 10 special
battles at the Monster Arena to obtain the Sigil is a lengthy endeavor. To
speed things up, buy monster-capturing weapons from the Arena as soon as you
reach the Calm Lands, and keep them equipped as much as possible.

Abilities: [Break Damage Limit] + [Triple Overdrive] + [First Strike] +
[Counterattack]

Special Effects: Does more damage when Auron's HP is depleted, and allows
Youjimbo to exceed 9,999 damage.

Edit: Sorry it didn't come out too good...

Yeah, I got Auron's Murasame too and customized it to something called "Dragonkiller" by adding some abilities to it. It's actually possible to get a whole bunch of Murasames, by fighting the monster in the Monster Arena that drops weapons with One MP Cost (don't remember which) or just customize it onto a weapon. Fortunately, as has been said, since it's not the Masamune, you haven't missed out on Auron's Celestial Weapon.