In FF7, to gain and learn the final limit break level, Level 4, you have to locate different manuals so the characters can learn the ability. As the prequisite, the character must have all the Limit Breaks learned that are possible to activate it. Second of all, the Character must have the specific limit break manual available.

Level 4 Limit Break Manuals
Character	Manual	Location
Cloud	Omnislash	Purchase At Battle Square : Requires 32,000 BP
Tifa	Final Heaven	Play The Song At Tifa's House In Nibelheim : Disc Two Or Three
Barret	Catastrophe	Old Lady In The Hut : After Saving North Corel From Runaway Train
Aeris	Great Gospel	Weapon Shop On Peninsula : Must Recieve Before End Of Disc One
Red XIII	Cosmo Memory	Defeat Lost Number In Shinra Mansion : When You Acquire Vincent
Cid	Highwind	Crashed Glenika : Use Submarine
Yuffie	All Creation	Defeat Godo At Wutai Pogoda : Yuffie Sidequest
Vincent	Chaos	Lucrecia's Cave : Vincent Sidequest