Key Items are unique, plot-critical objects that are essential for progressing the main story or unlocking new areas. These cannot be sold or discarded. Examples include the Folding Airship, Horn of Ice, Nepto Eye, and various elemental shards. Always pay attention to hints from NPCs about where to use these items. Accessories, on the other hand, are equipable items that provide various stat bonuses, resistances, or special effects. They are equipped in a dedicated accessory slot for each character.
Accessories can be incredibly powerful. For instance, the 'Protect Ring' grants immunity to certain status effects, while the 'Ribbon' grants immunity to almost all status effects, making it one of the best accessories in the game. Other accessories might boost a character's Strength, Intellect, or Agility. Prioritize equipping accessories that mitigate common threats in a dungeon or enhance a character's primary role. Many powerful accessories are found in hidden locations, side quests, or dropped by rare enemies, making exploration and optional content highly rewarding.