Source: VG Center
I translated this to the best of my ability, hope it makes sense!

The ultimate weapons of Final Fantasy X are received in several ways. You get the basic weapon but in equip you do not gain more AP. One needs then touver the 7 trunks containing the LV1 of each weapon, there you still do not gain a AP on the other hand a capacit�e news is added on this one. To obtain the LV2 (the weapon final) you must make a search for chaqu' one of them. Thanks to weapon LV2 you can receive the double of AP at the end of a combat and see news capacit�es to be added. Caution: To obtain the basic weapon it is necessary to gain the mirror and to make it magic . Then to pass it to LV.1 then LV.2 you must turn over to the place or you made magic the mirror.

Character: Tidus
Weapon: Ultima Weapon
How to obtain it: It is in top on the left on the plains of Nagi. You'll need to enter a small passage to go to speak to a man who prevents you from passing. To turn over to make the 4th race of chocobo on the plain, then the man who blocked the passage is not there any more, you can then recover Ultima Weapon.
LV.1: Ebon Dome
LV.2: You'll need to finish the last race of Chocobo in 0:0:0 (for that collect the most balloons possible).

Character: Yuna
Weapon: Nirvana
How to obtain it: You'll need to capture a monster of each species on the plains of Nagi for the Monster Hunter.
LV.1: Beside Island Beach
LV.2: Should be beaten your 8 Aeons with the Remaria Temple.

Character: Lulu
Weapon: Knight of Tamanegi
How to obtain it: Ebon Temple: In the lake.
LV.1:GuatoSalam, zone of deaths
LV.2: To avoid 200x continuation the lightning with Thunder Hill.

Character: Auron
Weapon: Masamune
How to obtain it: Before the cave of Yojinbo you will find a sword planted in the ground, take it. Then go in Kinoko canyon, take the elevator and plant the sword in the statue.
LV.1: South of the Mihen old man.
LV.2: Unlock the 10 special battles of the Monster Hunter

Character: Wakka
Weapon: World Champion
How to obtain it: Win the Blitzball tournaments in Lucca.
LV.1: In the rest room in the Blitzball arena.
LV.2: You'll need to play several games of Blitzball... (You will also need all the Overdrives of Wakka).

Character: Rikku
Weapon: God Hand
How to obtain it: In bottom of Kinokoiwa canyon after having brought Al Bhed Book to Line.
LV.1: West of Sanubia desert, in the swirl.
LV.2: You'll need to finish the search of the Pampas (Cactuar).

Character: Kimari
Weapon: Longinus
How to obtain it: You have to light the 3 stones of Pampas (Cactuar) at Thunder Hill, then find the Pampa ghost.
LV.1: Gagazeto Mountain.
LV.2: Second Butterflies mini-game at the Maccarania Forest.

Section from FFSphere

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