Character Weapons
To obtain the Treasure Hunter trophy, you must collect every weapon for game's six main characters: Lightning, Sazh, Snow, Vanille, Fang and Hope. Lightning's weapons are gunblades; Snow's weapons are emblems that augment his fists; Sazh's weapons are pistols; Vanille's weapons are rods; Fang's weapons are spears and Hope's weapons are boomerangs. Each character has 17 different weapons, for a total of 102 weapons that you must collect. The various first-tier weapons for each character can all be purchased or found at some point in the game.
Upgrading Weapons
Some of the weapons in the game can be obtained only by upgrading your current weapon. Upgrading your weapons requires both experience points gained from battles and components found while exploring. To upgrade your weapons, navigate to a save point and interact with it. Select the "Upgrade" option from the menu that appears, followed by the "Weapons" option. Select the component that you want to use to upgrade the weapon to upgrade it to its next tier.
Third-Tier Weapons
After being upgraded to their second tiers, all weapons in the game have the same third tier. To get the Treasure Hunter trophy, you only have to upgrade one of each weapon type to the third-tier level. This means that you need to have one third-tier gunblade, emblem, pistol, rod, boomerang and spear. You can upgrade your weapons to the third tier using experience points and items, just like when upgrading to the second tier. The third-tier weapons are Omega Weapon, Total Eclipses, Save the Queen, Nue, Nirvana and Kain's Lance.
Accessories
To obtain the Treasure Hunter Trophy, you must also collect every accessory in the game. There are 119 accessories in all, each of which can either be bought from merchants, found while exploring or obtained as spoils after a battle. These accessories aren't character specific. Accessories can be leveled up like weapons, but you don't need to level up any accessories to obtain another accessory.
Components
When a weapon or accessory is dismantled, it yields certain components that can be used to upgrade other weapons and accessories. You don't need to collect all of the components in the game to obtain the Treasure Hunter trophy. Collecting components will prove useful, however, because it will allow you to upgrade your weapons to their second and third tiers.