HMMM i think its that saki was into classical music First than Tsukasa and it could calm down Saki so well that he tried his best to learn how to play the piano even faster than her
When Toya was in distress as a kid, in the other hand, Saki tried to sing kids songs once and her voice could make him sleep so peacefully she tried to sing in choirs to improve her voice for the sake of toya even if her throat could hurt sometimes because of it. Between all the tenmas, saki has the most wise, but the one who actually does wise things is toya so saki kinda feels sad for it,,, toya always reasures her that he learnt all of it with her help and it was only because of tsukasa he could make his life choices that saki seems to admire sm