The wording on this trophy/achievement is a little confusing, as one might think you need to max out the levels of everyone’s weapons. However, that is not the case, as it pertains to the Weapon Shop, a shop you unlock automatically during Main Story 6: Trouble in the Quarry. Upgrading your weapons at the Weapon Shop will unlock new abilities for your characters, such as charge attacks, more hits for their combos and more. As you progress through the game, you will have more quests from the Weapon Shop, allowing you to upgrade them further. Note that these upgrades at the Weapon Shop are more expensive than the ordinary ones at the Smithy. Once you see the MAX upgrade, that will be the final one. Get the MAX upgrade for all three characters to unlock this trophy/achievement.