The Dumpty Key's real ability is said to unlock people's hearts so that they might understand each other's feelings and put their doubts aside. Since its companion is the Humpty Lock, their powers are very similar. Like Humpty Lock, it has the power to grant people the ability to Character Transform, which Ikuto uses to Character Transform into Black Lynx. In chapter 38 and episode 100, Amu puts the key into her Humpty Lock, and so is brought to the Road of Stars to see Ikuto's painful past. After she finally understood how he felt, she opened her heart to him, allowing the Dumpty Key and the Humpty Lock to turn them into Amulet Fortune and Seven Seas Treasure.