Im not sure of that girl playing the piano is Sachiko or Kanako, the hair kinda has the dempa look, but its not all completly right for Kanako.

On the other hand, Kanako and Touko do tend to be pictured together, regardless of wether it's in-character. Also, she's looking back sort of nervously at Touko, which seems more like something Kanako would do.

It's Kanako.

Notice Sachiko has her split on the left side and keeps the forehead hair /short/ and combed straight down to the side (post #47520), where as Kanako keeps hers /long/ and splits it in the middle going the ^^-type antenna look, which can still be clearly seen here (post #18877).
In this image she's just combed/drawn with her usual dangling front tails behind her back/ears.

A Same pic. Notice his sig in the lower left corner.