about the sigil, crest

[Guardians]

well, i get the weapon 1st b4 i get sigil and crest, now i already get the sigil and crest, how i power the weapon now?

[Cookie]

You need to get the cloudy mirror, power it up to the celestial mirror then take the weapon to the place where you powered up the mirror.

[feona17]

To get the cloudy mirror is a rather long process. Alright this is an excerpt, from a walkthrough on gamefaqs.com written by Blackestmage.
http://www.gamefaqs.com/console/ps2/game/197344.html

Calm Lands
=======================================================

Auron and Lulu will teach you a few things about the Calm Lands. Many
summoners have been giving up on their pilgrimage here. It was here that many
High summoners performed the final summoning to battle Sin. When you can
control Tidus, head down the ramp to your right. Speak with Maechen if you’d
like to hear more about these lands. As he’s done, keep going west to access
the plains. Now, let’s do a quest! You don’t need to do it, since it is
entirely optional. It would still help though. What we’re about to do is to
give Valefor(your Aeon) the opportunity of breaking the damage limit, meaning
that she will be able to exceed 9999 damage. You need the Mercury Crest
though, which was obtained in Besaid early in the game. So, in the plains,
buy some goods from the ship nearby and then, just head north, hugging the
left. It’ll be a long way but eventually, you will reach a cliff. Keep
running toward the right, and you should meet up with a Chocobo Trainer. She
can’t let you ride a chocobo unless you train one. Accept to do so. The
challenge will be quite easy; you simply need to reach the trainer at the
finishing line riding your chocobo in a time of 12.8 seconds or below. You
can only move your chocobo with Left and Right though. When you’re
successful, you get a prize as a reward, AND, you’re able to ride a chocobo
anytime in the Calm Lands. With a chocobo, go back to the entrance(from where
you came) but keep going passed it and check out for a broken bridge. There
is a chocobo feather nearby. Press X on it and your chocobo will fly to a
lower level. There, dismount it and head inside the path to the next screen.

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Remiem Temple
=======================================================

Cross the bridge, save(if you need) and follow the path to the left of the
castle. You will reach a chocobo and a sphere on the ground. Examine it(the
sphere) to learn that you can race chocobos here. You have to use the chocobo
on the opposite side of the castle though. There, examine the chocobo to
race! Simply beat the other chocobo by reaching the platform in the middle
before it and you obtain the Cloudy Mirror. Leave Remiem Temple afterward.

=======================================================
Calm Lands
=======================================================

Ride the chocobo again and jump off the level you’re on, back in the plains.
Open the two chests nearby and go back up the ramp West and enter the
Macalania Wood.

=======================================================
Macalania Wood
=======================================================

Use the save sphere and keep going to the next screen. In the four ways area,
take the left path. You enter a crossroad, but one of the path is blocked by
a Monk(Bevelle), so take the other path(the left one). There, you’re back in
the other part of the Macalania Wood that you crossed earlier in the game.
Grab the hilarious Jecht sphere on the ground nearby and keep going left. You
meet up with a kid and his mom. Speak three times to both and you will
understand that the father of the family is missing. Go back to the four ways
area(two screens away) and take the north path(where your party slept before
going to the Calm Lands). Talk to the man there and Tidus will tell him that
he saw his family in the wood. He leaves, so follow him to where you just met
the family. Talk to him and his wife three times each to understand that
their son has disappeared in the wood. Let’s find him! See that shimmering
path near the save sphere? It’s new, it wasn’t here as you first came in the
wood. Follow it. In the next screen, take a left turn at the intersection and
meet up with the boy. He found some magical plant. Accept to show it the
Cloudy Mirror and it will be changed in the Celestial Mirror. Afterward, the
son’s parents are back and thank you for reuniting them. Head back to the
Calm Lands.