In Final Fantasy VII, there are Ultimate Weapons that have higher abilites than regular weapons. Unlike most weapons, the ultimate weapons have Eight Materia Linked Slots, and they have no growth. Some Weapons are depend on the Characters health for the attacks to be at full power, or a certain stat to be high enough.

Ultimate Weapons
Weapon	Character	Accqusition
Ultima Weapon	Cloud	The Ultima Weapon is obtained by killing Ultimate Weapon on Disc 3. After you defeat him, you will get the Ultima Weapon. The Ultima Weapon's Damage depends whether or not the HP of Cloud is high or low, the HP Amount will determine Cloud's Damange with the Ultima Weapon.
Missing Score	Barret	Missing Score is obtained In Midgar, After you fight Prod Clod, and the steps before fighting Hojo. Barret has to be in your party to find the item, or not you miss it for good.
Premium Heart	Tifa	Premium Heart is obtained at Wall Market, in the shop marked 'Item'.
Princess Guard	Aeris	Princess Guard is obtained at the Temple of the Ancients, in the Clock room V.
Limited Moon	Red XIII	Limited Moon is obtained from Bugenhagen on Disc 3, before he Dies.
Conformer	Yuffie	Conformer is obtained on the Gelnika.
HP Shout	Cait Sith	HP Shout is obtained at 64th Level of Shinra Building.
Death Penalty	Vincent	Death Penalty is obtained at Lucrecna's cave.
Venus Gospal	Cid	Venus Gospal is obtained from the Old Man in Rocket Town.