"In case you didn’t know, “Hikoukigumo” was not written for Kaze Tachinu, as most Ghibli movie theme songs are. Yuming wrote it when she was 16. When Miyazaki heard it he chose it, saying that it was perfect for the movie.
Yuming wrote “Hikoukigumo” because of a very close friend she had since Elementary school. Her friend had a weak constitution and was constantly ill. At the early age of 14, Yuming started her singing career and traveled around, taking voice lessons and performing. When she returned to her home town and visited her friend’s house, she was greeted by a shrine and the news of her friend’s death.
In her sadness, Yuming wrote “Hikoukigumo” and recorded it, however it was never a success compared to her other songs. So when Miyazaki contacted her and told her he wanted to use it in his film, she was overjoyed.” — saotome-michi.tumblr.com