Final Fantasy X International (Import) Tips

Yuna (Nirvana) Celestial Weapon
You can get the Moon Crest from a chest at Besaid Beach.

You'll receive the Moon Sigil from Belgemine once you beat all her Aeons in Remiem Temple.

Here's a list of all the items you'll receive from her every time you defeat each of her aeons:

Valefor » Aeon's Soul / Lightning Gem x4
Ifrit » X-Potion x30
Ixion » Chocobo Feather x10
Shiva » Mega-Potion x60
Bahamut » Flower Scepter
Yojimbo » Shadow Gem x8
Anima » Stamina Spring x60
Magus Sisters » Shining Gem x40

If you caught all the monsters in Calm Lands, the Trainer will give you a chest which requires the Celestial Mirror to open. Get the Nirvana there.

Once you have the weapon and the necessary crest and sigil, go to Macalania Woods and examine one of the white orbs there to complete the ritual and maximize the power of the weapon.