Solution

From Shadowes

It's Chopin's Waltz op 64 n 2 in C#. Only, it is played on a mirror keyboard. That is, a keyboard on which low pitches are to the right, and high pitches to the left of the player. If you want a somewhat vivid image, think of the virtual pianist you see mirrored in front of you in the piano as you play. (Here is a midi version of the original waltz.) In the mirror play, inverse chords invert the mode. Hence the original minor mode is turned into a major mode. No matter what the differences, there is something dinstinctively Chopinian about the phrase!