Here is the overall story:
(I realize I am having a theme of crystals in my work lately! wow!) The Dwarf kingdom is dark that is lacking aesthetic
qualities that the surface world has. The Dwarf king reads a tale of the mythical nightingale that lives deep in the crystal forest. He calls in his lord in waiting and orders the capture of this creature. He imprisons the bird upon retrieval in magic crystal. He only releases the bird when he wishes the bird to sing.
As a gift, a neighboring kingdom sends a synthetic bird to sing. The song is mechanical and doesn't change from play to play. The nightingale escapes. After much use the synthetic bird dies. The king falls into a depression, almost causing the king to die. The nightingale had compassion on the king, he returned to sing a song of healing. Death was vanquished and a pact was made between the king and nightingale, the bird would sing for the king but only if he was to be free.