For those not in the know, in Final Fantasy VII (Playstation 1), for the very last battle against Sephiroth, your limit break gauge increases without having to do any attacks whatsoever (apparently powered by anger or something). Eventually it fills all the way and you do your limit break attack, which finishes off Sephiroth for good.
Note: Omnislash is the Level 4 (ultimate) limit break for Cloud Strife.
Edit:
Found a video that shows this exchange:
Updated