not on your list add 4.42 ✎ bu neng shuo de mi mi (不能說的秘密) 2007 (film)

Talented young pianist Ye Xianglun has just transferred to a new school. Although he is clearly admired by his friendly classmate Qing Yi, Xianglun is more interested in a mysterious girl he heard playing alone in the school's old piano room. Her name is Lu Xiaoyu, and when Xianglun asks her what the song was she had been playing, she simply smiles and tells him it's a secret. Xianglun notices Xiaoyu 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, Xiaoyu still refuses for a long time to teach Xianglun 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, Xiaoyu disappears altogether, and a confused Xianglun 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. Xianglun is perplexed, but one thing is clear -- until he discovers the significance of the song Xiaoyu played, the mystery will stay a mystery.