Sonatina can write and owns a slateboard so it is possible for them to communicate. As dark magic isn't too prominent in Valm, I guess Sonatina would be quite interested in dark magic and would like to see what it can do. As for the communication issue, Sonatina would probably take the initiative to come to talk to Wayra or watch him practice magic.
Honestly, I could only see their relationship as awkward. The lack of consistent speech from Sonatina mixed with Wayra's tribal thinking would be interesting. I could see Wayra being intrigued by Sonatina's illness, as he likes to understand how things work. One thing I personally can't answer is how Sonatina would react to Wayra's dark magic. Anything else you can think of?