Key items are unique, story-related objects that are essential for progressing through the main quest or unlocking specific side content. These items are usually acquired automatically as you advance the narrative. Collectibles, on the other hand, are optional items that you can find throughout the world. This includes Katz Spirits for Katz Boxes, various crafting materials, and 'Discovery Points' that reveal lore. While not strictly necessary for completing the game, collecting these items often provides valuable rewards, unlocks new features, or contributes to achievement completion. Always keep an eye out for sparkling points on the ground or hidden chests, as they often contain these valuable collectibles. The 'Library' section in your main menu can help you track your progress on various collections.
