The Treasure Hunter Achievement / Trophy is one of the most notoriously difficult to obtain, not just in Final Fantasy XIII, but across the entire Final Fantasy Series, and this is for two reasons. The first is that it involves collecting every item in the game and several of the required items are missable, so if you didn’t see a specific Treasure Sphere, you might be completely out of luck.
The second reason has to do with the challenge and cost associated with upgrading all of the items. This can be an expensive and, therefore, time consuming process as the amount of Gil you have to farm can be considered too excessive for many gamers. With a strategy guide, like this one, this process can be made much easier, but the fact that you almost need to have a guide to get this achievement / trophy has been a frustration for many players.
The actual achievement / trophy is earned by examining Bhakti in the Dilapidated Dwelling of Oerba. Bhakti will offer you “Bonus Bytes” when you speak to it and will let you know if you haven’t yet obtained all of the available treasure by stating “…But somewhere out there, long-forgotten equipment still waits to be found” meaning there’s something you haven’t obtained yet.
An important fact to remember is that you don’t have to actually carry all of the required items in your inventory at the same time. You just have to have had the item in your inventory at some point, so if you upgraded an item or dismantled an item, it will still count as having been “obtained” for the purposes of this achievement.
Obtaining this trophy will require you to upgrade your equipment and use catalyst components to transmute that equipment into its next level. For example, Lightning’s weapon 
Blazefire Saber requires 24,600 experience in order for it to reach its maximum () level, at which point you can use a 
Perovskite catalyst on it to transmute it into a Flamberge. After another 449,310 experience, it can be transmuted one more time using a Trapezohedron into Lightning’s Ultimate Weapon, Omega Weapon. In order to obtain the Treasure Hunter trophy, you will have to have had all three weapons.
For more information on equipment upgrading, check out the tips and tricks section:
As noted on the Upgrading Equipment page, all weapons upgrade to the same weapon for each character when you use a Trapezohedron on them. All of Lightning’s weapons upgrade into an Omega Weapon, all of Hope’s weapons upgrade into a 
Nue, etc.
You only have to upgrade one weapon into their Ultimate Weapon and, for characters you don’t use often, you should choose the weapon for them that is cheapest to upgrade (i.e. requires the least amount of experience).
The guide for obtaining each piece of equipment will outline what components need to be used in order to obtain each item’s upgraded form. Start by using the organic components, such as 
Sturdy Bone, Barbed Tail or Vibrant Ooze (all of them cost the same and have the same effect), then use the required mechanical components, such as 
Superconductors, Particle Accelerators and Ultracompact Reactors. Using the correct number of components is critical in making sure that you don’t overspend your Gil and have to farm any more than necessary.
Using organic components will raise up the experience multiplier, but each time you use mechanical components the multiplier will drop back down. This means that you should use all of your mechanical components at the same time, otherwise you will have to use even more organic components to get the multiplier back up.
To get an idea of how much farming you will have to do, you will need the following catalysts:
Adamantite (x5)Cobaltite (x4)Dark Matter (x5)Mnar Stone (x1)Perovskite (x37)Scarletite (x12)Rhodochrosite (x1)Trapezohedron (x6)Uraninite (x20)The Trapezohedrons and Dark Matter have methods you can use to farm them in battle though so don’t let the price tag on those components panic you just yet!
You can use the checklist compiled at the following Google sheets URL to track which items you have obtained:
[Google Sheets]The list below includes all of the weapons and accessories that you need to obtain and how to upgrade them. Click on the weapon or accessory for more information on where it can be found or purchased:
[Upgrade List]
