Quote Originally Posted by Guitar from blackness
here are some steps i used

1.Curaga
2.Having L.3 limit breaks
3.Reflect
4.Double cut materia
5.Increased magic defense

i dunno if if this can help but im glad if it does
Huh? Anyway, here is something posted ages ago about Ultima Weapon and all stuff, it is a bit long but the info is precise:

http://forums.eyesonff.com/showthread.php?t=53904

You can kill Ultima Weapon with one Lionheart limit break if you are lucky.