There are a variety of keyblades you can get in Kingdom Hearts 3 but there is a secret one that doesn’t unlock from merely completing a game world. To get the Ultima Weapon, which is the most powerful keyblade in the game, you’ll first need to complete a few requirements that will then enable you to craft it.
In order to craft the Ultima Weapon keyblade, you must gather 58 Synthesize materials. If you’re not familiar with these, you’ll want to visit the Moogle Shops’s Workshop section. In there you can either synthesize items, use the Keyblade Forge to upgrade your keyblades, check Photo Missions and Collector’s Goals, or view the Materials List. Explore these menus and get familiar with the various Synthesize material names that you’ll need to collect. A lot of them are collected from items you get during the main story but you can also run through Battlegates and revisit worlds.
The materials you need are:
With these gathered, you can enter the Synthesize Items menu and select Ultima Weapon to craft it. Doing so will ear you the achievement: Ultima Weapon and is also required to earn Blademaster; which you get for collecting all keyblades in the game.
While all the materials have some difficulty to collect, Orichalum is certainly the harder one. To help, here’s some ways to earn this rare material:
Purchase a Moogle Raffle Ticket for a change to win Orichalum as one of the prizes.
Mailing off postcards gives a chance to receive Orichalum as a reward.
While exploring the Eclipse Galaxy in your Gummi Ship, there’s a Space Monster boss that rewards Orichalum.
Collect all the treasures in the Snow Sliding mini game to earn Orichalum as a reward.
One of the treasure chests on the smaller islands in the Caribbean level has Orichalum.
Earn the high score in all 7 mini games for the 7 princesses will reward you Orichalum.
Collect all the Lucky Marks and you’ll get Orichalum as a reward.