1. In both drama leads are in reverse loop of time.
2. Both drama end in separation.
3. Ancient love song has a bit tragic feel while unspeakable longing is lighthearted.
FL also travelled from modern world into a fictional world
In both drama, the original plot has ML disliking the FL and is a requirement for FL to change this by making ML fall in love with her. The task is a tall order but the only way to survive and return to her own world.