One of the recipes in the game that you can unlock will allow you to create something called the Supreme Sword of Light. In order to get this recipe, you will need to do the Drustan Trials and defeat a boss at the end. Once you do, you will be granted a wish and one of those will allow you to get the recipe for the sword. If you’re looking to forge it, you will need to do a few things, so visit the Supreme Sword of Light page to find out more information.