My Sassy Girl (엽기적인 그녀; literally, That Bizarre Girl) is a 2001 South Korean romantic comedy film directed by Kwak Jae-yong, in which the lead protagonist's chance meeting with a drunk girl on the train changes his life. It is based on the true story told in a series of love letters written by Kim Ho-sik, a man who initially posted them on the Internet and later adapted them into a novel.
Also, the main theme is great
I Believe - Shin Seung Hun
It's a great and lovely film. I recommend it!!