you have to win the final 1 in the golden saucer. hit about 5 limit breaks with could between each level

you go to the gold saucer and go to the battle part (you will need alot of gp) then win a
few times and you should be able to buy it. All the others you just earn by fighting and
using his limit break as much as possible. thank you and g'day!

1st limit: start game with this
2nd limit: use braver 8 times
3rd limit: beat 80 enemies after getting cross-slash
4th limit: use blade beam 8 times
5th limit: beat 80 enemies after getting climhazzard
6th limit: use meteorain 8 times

7th limit (omnislash): in second or third disc, get 32000 battle points in the golden
saucer and trade it for omnislash (must have the other 6 limits in order to actually
learn)