Any character whose hit points are reduced to 7777 after an attack gets all lucky 7's effect. The character goes in to a mad rage and begins attacking the enemy non-stop landing a hit for 7777 points of damage each time. To get this you must first get your characters HP over 7777. this means all lucky 7's affect can only happen to high level characters, or those equipped with several hp plus Materia. You must also be very lucky since a attack must knock that character down to exactly 7777 HP. it can happen but its not likely to happen when you want it to. Also after a battle where a characters hit points are 7777, that characters HP is reduced to 1. So you cant carry this effect over in to another battle. I have not yet found a way to get this effect by equipping Materia and equipment, but that's not to say that it cant be done.
Voilà un exemple de 7777 sur un perso non jouable