Nana, Kagen no Tsuki Recommendations
Also one of Ai Yazawa's work, Nana holds one or two references to Kagen no Tsuki. Both stories have love and music in them, though Kagen no Tsuki is also paranormal and holds a secret you find out at the end. Nana is more realistic and focuses it's story more on the feelings of the characters. Kagen is much shorter than Nana, but both are very enjoyable.