From Comiket 74, somebody gave this to me and it was just too awesome not to upload.
For those who don't know, this is a remix of U.N. Owen was Her? from Embodiment of Scarlet Devil, which is part of the Touhou Project, a series of shoot'em up games created by ZUN. This is the main theme of Flandre Scarlet, the Extra Boss.
*For the record, I screwed up making this video and it lasts a few extra seconds and I couldn't check it since my computer sucks and wouldn't load the video without crashing. I was thinking about re-uploading it, but it doesn't seem worth it just to remove like an extra 10 seconds.*