Celestial Weapons are powerful weapons that the character can get as part of various sidequests in the game. However, just finding the weapon isn’t enough, as each weapon will have a Crest and Sigil needed in order to unlock its full potential. So, you will need to find the weapon, as well as the Crests and Sigils. When you first find a Celestial Weapon, it will come with the No AP auto-ability on it, which is a bit useless. However, by applying the Crest to it, the weapon will gain the Double Overdrive auto-ability, in additional to No AP. Applying the Sigil will get rid of the other two abilities and fully power up the Celestial Weapon, with each character getting their own set of abilities.
The Celestial Mirror
In order to fully unlock the Celestial Weapons, as well as even collect the weapons themselves, you will need the Celestial Mirror. Note that the Crests and Sigils do not require the Celestial Mirror, so it is possible to start collecting them as you come across them. You won’t be able to start the sidequest for the mirror until you have reached the Calm Lands. Once you have, you will need to complete Wobbly Chocobo in order to unlock the ability to ride chocobos on the Calm Lands. When you’ve done this, head to the top of the giant hill at the entrance and on the right side is a chocobo feather that will bring you to Remiem Temple.
While at the Remiem Temple, go to the right side and do the race there. You only need to beat your opponent, without needing to open any chests, to receive the Cloudy Mirror. With that in hand, return to Macalania Woods and find the first Save Sphere on the southern side of the woods. There should be a mother and child at the fork there, so speak to the mother to find out that the father is missing. If you remember where you ended up right before you entered the Calm Lands, you will find the father there. It’s the screen to the north at the four-way intersection before leaving to the Calm Lands. Speak to the father and tell him “they were waiting over there.”
He will return to his wife and child, so head back there now. When you find them again (same spot as before), you will see the child is missing. Speak to the mother twice for her to tell you her son ran off, then follow the crystal pathway. At the three-way split, go up and you will find the boy by the dead end. Speak to him and you will get a prompt to hold up the Cloudy Mirror. Do so and you will automatically obtain the Celestial Mirror.
Celestial Weapons are special weapons, not just because they come with preset abilities, but they also have some special properties attached to them. For example, all Celestial Weapons come with Break Damage Limit, so you will be able to deal more than 9,999 damage, which will be needed to complete a lot of the Monster Arena and harder fights. Outside of that, all Celestial Weapons ignore defense, but they don’t have Piercing for the armored monsters. So, if you were going to make your own weapons, then you will be missing out on that defense-passing property. Additionally, all of the Celestial Weapons have a special mechanic related to the characters’ HP or MP, as follows:
|Tidus||Caladbolg||More HP for user = more damage|
|Yuna||Nirvana||More MP for user = more damage|
|Rikku||Godhand||More HP for user = more damage|
|Lulu||Onion Knight||More MP for user = more damage|
|Auron||Masamune||Less HP for user = more damage|
|Wakka||World Champion||More HP for user = more damage|
|Kimahri||Spirit Lance||More HP for user = more damage|