CMX's library never fails to surprise me, even after all these years. Their library was filled with interesting little shojo series like this.
VS. (Vasasu), by Keiko Yamada. First published in 1999 and first published in North America in 2006.
Reiji is an incredibly talented violinist who is driven to succeed so that he can save himself and his sister from their abusive father. His playing is technically accomplished, but often lacking in emotion. Thus, his teacher calls upon the assistance of Mitsuko, a former student and violin prodigy whose career was cut short by an accident. The two of them are frequently at odds, as Mitsuko tries to find a way to connect with Reiji while Reiji fights to save his sister before it is too late.