Key item

Key Item
Key items are special items that players can only obtain once, and either aid the progression of the storyline or allow access to new areas and sometime friends or characters in the game give them to the player.The items cannot be bought or sold at Poké Marts, disposed of, or given to Pokémon to hold. Since Generation two, these items have been given their own classification and have been stored in a separate pocket in the bag. They are usually obtained throughout the storyline and are given to the player by other people. Once a player has obtained a key item, there's no way of getting rid of it unless it is part of the main storyline.