Open Heart is used when Amu Hinamori Chara nari into her would be selves Amulet Heart, Amulet Spade, Amulet Clover, Amulet Diamond/Dia. Open Heart is used to cleanse X-eggs, X-characters, ? eggs or ? Chara Nari. Open Heart can only be used by Amu Hinamori since she is the only one that has the Humpty Lock.