not on your list add 4.21 ✎ bu neng shuo de mi mi (不能說的秘密) 2007 (film)

Talented young pianist Ye Xiang Lun has just transferred to a new school. Although he is clearly admired by his friendly classmate Qing Yi, Xiang Lun is more interested in a mysterious girl he heard playing alone in the school's old piano room. Her name is Lu Xiao Yu, and when Xiang Lun asks her what song she was playing, she simply smiles and tells him it's a secret. Xiang Lun notices Xiao Yu is often absent for long periods of time, but when she returns she always insists she was just off practicing. Though they become quite close, Xiao Yu still refuses for a long time to teach Xiang Lun the song she was playing on the day they met. When she finally does, she makes him promise not to play it in the old piano room. Not long after, Xiao Yu disappears altogether, and a confused Xiang Lun is left wondering. After looking desperately for 4 months, he finally catches a glimpse of her, but she disappears almost as quickly as she came. Xiang Lun is perplexed, but one thing is clear -- until he discovers the significance of the song Xiao Yu played, the mystery will stay a mystery.