Craft a 7 Star Weapon
Weapons have a star rating based on their overall quality and level of parts. When crafting weapons you can use high-quality parts along with upgrading the quality and material of a weapon at a bench to try and make a 7-star weapon, but that takes a lot of materials and requires finding high-quality parts first.
An easy way to do this is to first obtain the Pri Murgel Sword, which is one of the best melee weapons in the game. You can obtain it by first going to Lumentower on the southeast corner of the world map, climbing the tower, and activating the lighthouse light to point you towards a hidden cave with a new sidequest.
Follow the objective, and in the cave, you need to activate the 3 sections on the walls with writing on them to obtain the sword. The sword starts out at a 5 and a half stars rating with maxed-out quality and material. To get it to 7-star rating you just need to craft two add-ons into it. You can buy addons from the melee merchants at any outpost (the smith on the right side after entering a captured outpost). You can also find Addons in the world. When you buy them, make sure to buy those with a 1 star rating. Adding 2 x 1-star addons will bring the weapon to 7 stars total.