The Legend of Zelda: The Minish Cap/Items/Kinstone
Kinstones are special artifacts first introduced in The Legend of Zelda: The Minish Cap which Link can find throughout his quest. They are kept in bags called Kinstone Bag. You receive the bag for free after you completed the first dungeon. Kinstones are generally green, blue or red although they can be gold if they are '"fused" with the wall.
By pressing L, it allows the player to "fuse Kinstones" with non-player characters (NPCs) in the game. Two kinstones with complementary shapes be combined to form a coin. If the player can find the NPCs who possess a kinstone complementary to his, he can perform Kinstone Fusion, which causes special events to happen. For example, fusing Kinstones can reveal a secret passageway in a different area, or make a treasure chest appear.