Song: Sasori No Harawata
Instrument : Piano (to be more precise I would like to play it on my keyboard but with an organ sound instead (I hope I'm not asking too much))
Anime/Game: Umineko No Naku Koro Ni (Visual Novel)
Artist: Luck Ganriki
Album: ~Rose Crimson~

Comments:

Here's the song itself
http://www.youtube.com/watch?v=2-5JlUoVuYc

I would be eternally grateful to anybody who could write down this beautiful piece.