Each of these characters has a set of unique abilities called LIMIT BREAK and preferred weapon types.
LIMIT BREAK
This is a special set of abilities that a character can use if their LIMIT Bar becomes full. This bar fills as the character takes damage and, when full, they can unleash a powerful ability that, depending on the character, will either be offensive or defensive.
Each character has a number of abilities that they can learn via various means; number of enemy kills, number of times a previous LIMIT BREAK has been used or by items. They are split into Levels; 4 levels in total (with only Cait Sith having 2 Levels); and each level has 1 or two abilities.
Weapons
Each character has a preferred type of weapon; each weapon has various stats that relate to the offensive stats of the character. Some have slots on them to attach Materia and most that do offer Materia Growth bonuses that can double or even triple the growth of attached Materia but a few offer no Materia Growh at all.
Some are available for purchase in shops, some are found and some are rewards from Boss fights.