What is the 'C' key again?

Okay, third drawing. :3
Like my previous drawing, this is basicly a drawing for someone, it is for pg2125 with a pretty much the same reason like the other one. xD
I drew Luka for him because I think he likes Luka a lot. xD

Luka is trying to do the 'C' key but have no idea how to do that... so her hand is just close to do the 'C' key.
While rin, she just there... sleeping beside Luka. xD

By the way, Luka isn't wearing a santa hat or a nun hat(like in Palette song) though.
It is just a normal cap that pg2125 usually wears everyday (maybe.. xD). The guitar Luka is playing with, is also pg2125's guitar actually. xD

About the proportion and pose... I think it's messed up here and there...
Well, it is my third time drawing a character crossing legs (the other 2 are my old works and it's really suck. ), and I'm having trouble to draw something that looks like 45 degree toward us, which is her left hand... so, sorry.

Special thanks to :
My classmate, Devit, to show me how the C key is looked like.