"Jace was seated at the grand piano, his slender hands moving rapidly over the keys. Watching the quick, sure movements of his hands across the keys, Clary remembered how it had felt to be lifted by those hands, his arms holding her up and the stars hurtling down around her head like a rain of silver tinsel. ~The City of Bones Pg. 62
"Tessa watched in amazement. Jem began simply, softly, his grip light on the bow, producing a soft, harmonic sound. The melody rolled over her, as cool and sweet as water, as hopeful and lovely as sunrise. She watched his fingers in fascination as they moved and an exquisite note rose from the violin." ~The Clockwork Princess Pg. 184
If Jem and Jace could create music across time, a tribute to their lovers, from the end of the beginning to the start of a new era, this is what I imagine their song might sound like.