I was playing Team Fortress 2, and some guy was playing this over the microphone. I asked him where to get it, and he told me. This is totally awesome.
Sadly, I can't embed it on Youtube (because it's 20 minutes long), but you can have the 45-megabyte MP3.
Faster mirror: http://bunnitude.com/misc/files/sfc_genkidama.mp3